Hi. Good afternoon, everybody. I think we'll make a start.
Obviously, a few people are still filling themselves up on lunch. I'd like to congratulate you on making it halfway.
I think we may have lost one or two people by now, but some of you are still here for more activities.
I'm going to talk to you about diagnostic reasoning. I think it's interesting.
I have one mission in this talk. You know why some people are going to achieve lots of things.
I'm going to teach you about this and this and this. My mission with Julie Ashwood.
Julie said to me this morning, I'm not really into diagnostics and I'm not really into the teaching of it.
Even more so, my mission, apart from mission two,
I'll tell you Mission two is is to try and change your mind about diagnostics and try and change your mind.
The second one is, at some point I may roam around the room and I have to try and get Olive in the shot at some point.
Okay. About five years ago,
I came on this course and somebody was delivering this talk from diagnostics
about this time in the afternoon and I was sat the a mike Crowley is there so
fiddling around with my bag and after about 5 minutes I started to switch off
and do something else because all the information was going over my head.
Okay. So what I decided then was I thought,
I'm going to start thinking about this and what I'm going to talk to you about today is if you join me on this hour,
I'm just going to talk to you about things I find useful in my practice.
I'm not going to talk to you about fancy calculations and how difficult,
but I'll show you the simple bits are you and I want you to keep that in mind.
Often what happens here? People teach you research methodology and you get lost.
So to illustrate that point, this is my daughter, Katie.
And as you can see there at the back, they were discussing about the calculation, she's only five years old.
And in our house we like to keep things simple. And she's calculated a mean difference there.
And for the sharp people this morning, it was in Amanda's lecture.
You'll realise here she's got the confidence interval in. However, in our house we really like to do it well.
So here at the bottom is my eight year old giving her a bit of advice and how to get it right.
But it's important we have to and I've been doing that in my group is keeping things simple so we can understand them.
What I did, though, is I said to people sometimes and some people want to teach her.
Sometimes I put things on my slide in yellow that allow me to remind to just a reminder to me to do something.
I'm going to give you an illustration of diagnostic reasoning.
Actually, in practice, about two months ago, my daughter was ill in the eye and I've been in training now for eight years.
I've been qualified eight years. And you get to that point where you suddenly think, Oh my God, I'm not quite sure if she's really doing well here.
I'm really quite worried about my daughter.
She had diarrhoea, tummy pain, fever with 41, and I'm going, Oh my gosh, you might want to go and tell me what to do.
Now I'm sure those of you with children will recognise that from position.
So actually what I did do is bring my general practitioners in the morning and board with the receptionist.
Difficult not to mention the word.
I'm a doctor, by the way. And she went, Oh, right.
Okay. What we'll do is we'll get you a phone call. Now, I'm at 19 Beaumont Street and actually the person who then spoke to me on the end of the line,
if polled there at the back it was practising that day, you might have even forgotten it by now.
So he gives me the advice he talked me through when I'm feeling a bit more relaxed.
And then he says to me, What about the jump test?
And suddenly bang in my mind came back. The scenario I remember in my training there was this thing about rebound.
And if you've got this acute abdomen, these ask questions like, What's it like in the car or in a child?
What's it like if they jump up and down? And what happened is a minute earlier, she'd just come down the stairs and,
you know, like children do, they just jump off the end of the steps, don't they?
And I immediately relaxed. I said, Well, gosh, I feel better.
I can manage this. And did the phone call that afternoon.
She got better. Fever subsided. She felt better. You know, children instantly.
The better the running the bell. However, that evening, about 5:00, I suddenly said to myself, where is the evidence for that?
You know, I'm an evidence based practitioner. Let's do some deliberate practice.
So I actually looked it up on PubMed. The advantage of PubMed, you can do it in your own home.
Took me about a minute to find the article. In fact, in the acute assessment of children, the jump test is completely useless.
I thought, right. The next day I'm back to work.
I'm running to the office. By the way, Paul, do you know that assessment of the jump test?
He said, I know. I said, What do you mean, you know?
And he said, Well, I looked it up on my phone. It's completely useless.
That's how we think. Okay. That's evidence based practice thinking.
If feel you use that information.
Questioning your uncertainty. Okay, so we're going to have a bit of fun in this session.
Okay. I will stretch the time to the point when I start to think you're all slightly going to sleep and I'm losing you.
I will finish immediately then, if I think we're doing very well.
I'll carry on. Okay. Two things.
I've been having a lot of fun with Amanda with this.
I think the first thing is in diagnostic skills, we have to accept that there are things we do not know out there.
And the second thing is the way we perceive information can be faulty.
I'm going to deal with the second one and then I'm going to talk about strategies that can improve what we do.
Okay. You've all got this picture up and some of you should have this picture.
Now, if you look at this checkered square squares marked, B, are they the same shade of grey?
How many? No. Hands up. Okay.
Most of you. How many think? Yes. One or two or three.
Okay. This is an illustration of our perception now.
Somebody has got one of these sheets, have the. And I borrow your sheet there.
Sir, if you don't mind, I want you to just do something. If you start to follow the sheet over and bring A to B and then match the shading,
what you should start to see is that actually A and B are identical shades of grey.
You can take this away with me. Great.
Olive. Disagree. Can you just come down here with your paper, please?
On the right. Now this. Might you take it away? And however much I looked at this left down slide, I still think I used different to be.
Okay. You can take that away with. You can. Okay.
I'm going to show you a second one. That's even more fun. Okay. Okay.
The car picture. Are these cars the same size?
Now, you all think I'm playing tricks now? I could be doing this. Did I look the same size?
Okay, I think that's important because this is how we see information.
So when I look at my when I make mistakes in diagnosis, I can't understand sometimes how I've made the mistakes,
but information is presented to it's the same information. So when I measure these cars now watch where the wheelbase.
What happens to the wheelbase? You see that?
I'm going to move to the side as the wheelbase got shorter or longer.
And what about that? So say no matter how much I look at this, I cannot explain why that the same.
However, the information surrounding the cars is in perspective and different, and it's making you look at things differently.
So the context we see a person affects how we see them in terms of diagnosis.
If I see them in general practice, they're less likely to have a heart attack than if I see them in in the emergency department.
The context of the information is actually going to change what we do.
So what we did about three years ago is actually on a on a train about three years ago,
I thought there has to be more to diagnosis than what is just a two by two box.
And I was on a train with Paul and we started to flesh out what the strategies are.
And I want you to think of the strategies just like I did then as measuring effects, trying to improve the way we do things.
And I'm going to talk to you about a piece of work that we've been ongoing for about three years, about what I think evidence based diagnostics have.
I may lose you at some points. And if I'm losing you, you can do what Amanda did and just put your hand up and shout at me.
Okay, so let's stop.
I want you to just imagine this is me as a GP Monday morning in the clinic, feeling a bit tired in need of my first cup of coffee of the day.
And I have a message on my screen. There is a child coming in who is on well with a fever.
I have booked her into your emergency slot now.
I want you to just write down the one thing or two things that come to mind in terms of what the diagnosis is.
I'm going to give you 10 seconds just to write this down. If you don't know anything, that's fine.
Okay.
As you pop out for your next patient, hoping to see a cup of coffee out there, you ask the receptionist if there was anything else about the show.
Nice receptionist says to you. Oh, yes. Her mom said she had a rash or has a rash.
Okay. Write down the one thing that comes to your mind. You don't have to be a clinician here because remember, we're all parents.
We all do this diagnostic every day. Okay.
Number three, a child comes in to see a three year old is cries all for those?
That's a runny nose. It's had a temperature for two days of 39 degrees.
Three. The mom tells you that you check the temperature. The rash began this morning and is on the body and it's on the face.
Write down what comes to mind now. Lots of you writing down only a few people activity wise.
Okay, that is the rough. You say I want to look at the rough. That's the rough bit.
Slightly out of focus. Write down.
What? What? Some people are looking at that going, Oh my gosh, the GPU's at the back of the room are going.
There we go. Okay. Before you discuss with the mother what you consider the diagnosis to be, you ask her what she thinks it might be,
and the mother says to you, Well, I'm particularly concerned because at nursery at the moment, there's a lot of children with chickenpox.
Write down what you think the diagnosis is now. Okay.
So let's start here. What did people put down here as a possible diagnosis?
Only one piece of information such as urinary tract infection, infection, flu.
Tonsillitis. Meningitis.
Anyone with any viral illness. Okay, so simple pieces of information.
Single pieces of information. However much you think nothing's going on is setting off a trigger already in your mind.
Immediately. We're starting to think diagnostic strategies.
Okay. You got the second piece of information. And what do people think now?
Measles. Measles, meningitis.
Okay. Wherever I've been. That's about the two two particular diagnosis that everybody jump forward is particularly the meningitis.
Particularly apart from emergency departments, where now they're completely lost.
But everybody goes in that direction. Okay. Got this additional information.
What do people think then? Chicken pox.
Measles. What did you think? Chicken pox. Anybody else think chicken pox at this time?
One, two, three, four, five. Okay.
That's a classical textbook definition of how you diagnose chickenpox.
Okay. That's exactly how it appears in the textbook.
That's what we teach people. Only four or five of you actually could recognise a.
What about this? Okay, a lot of you are now more certain.
Okay. And what about when the mother said she had chickenpox?
Oh, she was worried about the nurse. Does anybody what do people think it potentially of now?
Okay, I'm going to illustrate. So what we've done there is we've used what are called the initiation strategies, initiation of the diagnosis.
You've used for possible strategies to initiate the diagnosis, the spot diagnosis with the picture.
Some people can immediately key into the spot diagnosis.
The self labelling patients or the professionals will ask you or tell you there is a particular thing they are concerned about.
Can you look at this patient? I'm concerned. They have cellulitis. I'm concerned about having a chest infection in this case.
The mother was concerned about other children with chickenpox presenting complain does set off of actual strategy.
But what you could see at the presenting complaint stage is you got a wide variety of possibilities.
And then actually we got this pattern recognition trigger. It relies on a particular memory.
Only a few people have some memory of that. Recognises the actual pattern of chickenpox.
Okay. So we've actually done this, we've gone forward as an actual piece of work actually with our GP's in Oxford to say do these exist?
And actually this is just a piece of diagram where they collected 50 new cases and said What initiates the strategy?
Each circle represents one of the gaps and as you can see, if they add up to more than 100%,
so you use more than one strategy at any one time to trigger the possibility.
So you can see here. Now, this is important. About 20% of diagnoses in primary care rely on a diagnosis.
Now, Mark, you're an undergraduate or a teacher in general practice.
How much diagnosis do you think we actually take in the medical education?
A law that I never had any teaching of spot diagnosis.
One in five of my presentations rely on some instantaneous recognition of the problem.
I like this self labelling. In fact, actually and I'll come back to this put in the when I did this with the emergency department registry,
I actually believe that you would ask the patient in some way they would be correct.
Okay. They said the only time they took notice of self labelling was when you actually
got right to the end of the consultation and you had no idea what was going on.
Then it was worth actually asking the patient. You can see here, presenting complaint always triggers off some hypothesis almost quite a lot of time,
and the pattern recognition is actually a smaller component, but it still exists.
Okay. So I want you to do this one more. Go at this.
This is actually this is last week in practice. Last Monday, this is Miriam, an eight year old.
So I want you to think of the four possible strategies. And then soon as you come up with a diagnosis in your mind, I want you to put your hand up.
So Miriam comes in to see me. She thought, what's? And you know, and you go out to get the patient and she walks in a little bit slowly.
Not too bad. Doesn't look, but, you know, hunched over a little bit, comes and sits down.
Okay. And I say, you sit there as a GP and you try and not say too much and you sit there and I go, okay, Miriam, what can I do for you?
And she said, I've got a problem with diarrhoea and a bit of flu.
And I've not been feeling too well. I'm listening, and I'm trying to encourage you not to interject.
And I've got back pain. I'm going.
Okay. Tell me about the back page. That's been pretty painful, actually.
It's down in the lower bit here. Nobody's got the handle yet.
You're all cagey. So I've got this. Oh, Paul's got his hand up.
Good. I've got the back pain here, and it comes around the side.
I think diarrhoea, gastroenteritis, old lady back pain.
And it comes around the side. I said anything funny about this?
She says, yes, and I've got a rash as well. Another person putting their hand up.
Okay. I said, What about this? She said, Well, it's tingling.
Okay. The more hands are going up. And so I said to her, So what do you think?
I said, Can I have a look at this rash, if you don't mind? Okay, there's the rash.
And then I asked her, What do you think it is? He said, My husband had something similar to this.
I think it was called shingles. Okay.
So some of you then. And that's the example there. That's how I think.
Did you see what was happening? Was going in the wrong direction in the first place with the diarrhoea and the gastroenteritis?
I was thinking, this patient has gastroenteritis. I shifted focus.
Because she said back pain. Back pain can come with abdominal pain.
You start to get a bit more worried. But then she starts a rash.
We get in a pattern, a period. And I had the tingling and some people went bang.
Some people can look at that and go, that is shingles can look at a patient and say, that is shingles.
Some people have never seen it before. And then when she qualified it by saying, My husband have it.
We can build the information off of how I think initially and that's the end of my diagnosis, in fact,
because I shut my mouth for 2 minutes and thought about where my strategy for that's the end.
I can then move into the consultation about what we're going to do for this patient.
So that's the initiation. Okay, I'm going to get you to think now,
but you've got some I'm going to give you an activity for a few minutes just to illustrate some of these points.
So at the moment, you've all got this little quiz. So I'm going to give you about 2 minutes.
I'd like you to just have a go at this quiz.
Now for the highest scoring person in the quiz, I have two copies of the User's Guide to the Medical Literature to give away.
So there's an incentive. These are not by Blackwell's, by the way.
They can't buy them at the bookshop. Okay.
Good, good. Now I need to remind myself of the questions.
Question one Was this here is this.
John four Give yourself a month. If you put John for all, inspect them off.
I'll give you a mark for inspect them. All he's got here is John four.
You'll have to agree with that. What neurological condition does John feel forth have stuck with about Parkinson's?
Because I call foot drop. Give yourself a mark. If you've got foot drop, how many people got foot drop?
All people. How many people? Watch Inspector Morse. Now, you could have a mark for polio.
Lots of you. Now, John, for every episode walks like this.
The cameras caught him off, but he walks like this. He had polio as a child and he got dropped.
And if you're watching another edition, you'll see walks like this. The camera often cuts him off there.
But if you don't know that to spot that, you will not be able to get that.
Okay. The next question. Question three What's this?
PADGETT Well, we know we're going to get full.
The question for what bridge is this, which is okay.
And the question five is, which is the nearest pub, my favourite pub, apart from the white horse next to Blackwell, the Turf Tavern.
If you haven't been down that street, you can't recognise it. You see that if you have been down that street, you can instantly recognise that.
If you haven't been to the Turf Tavern, what you should consider going there before you leave.
It's a very nice place to go for a drink if you can find it. But that's a good illustration of what I call a spot diagnosis.
There's no either or. You can't make it up. I can't give you additional information.
You either do know it or you don't. So there are lots of areas in your in your when you go back to your health care,
whether it's midwifery or nursery or it's in general practice, where you can say, actually, what are the spot diagnoses?
Our students need to know. Remember the 20% an experience will gain them.
Question six What's this? Okay.
Question seven Is the building what's this?
Divinity school? The divinity school. It's part of the Bodleian Library and it's been in Harry Potter.
Okay. I, too, have some discriminatory questions in case you're really smart and you've done this before.
And the last one. It's conjunctivitis.
Okay. Anybody score ten, nine, eight.
Gotcha. I'll make an easier test. Seven, seven, seven, six, six.
For Mike and another chap at the back there.
Congratulations. Now, if you give that one to Mike as well.
Now, it's an important point. I wanted to do that just to reinforce about the issue of spot diagnosis.
It's about experience. You can all see that you have to see these things.
You have to see these things in practice to know what you're doing. Okay.
Self labelling by patients in GP consultations. Let me get up to 50 cases.
This is what patients often came in with tonsillitis.
I've had it before, Doctor, and I've got tonsillitis again. I have a chest infection, Doctor.
I'm sure we'll all recognise. I don't. I have a groyne strain.
I have. Most people know when they've got growing ankle sprain.
That's primary cold. I have asthma. Even new people who've never had it before.
And I have a UTR, just like the last time. This is women.
So this is an interesting one.
If you have a patient who labels themselves as having a urinary tract infection, a woman who's had a recurrent urinary tract infection.
How often are they likely to be correct? So that's this is going to be now an interesting question that I asked, because this is what happened.
Okay. We formulated a question like we know know how to do it slightly different.
Here we have the indicator or the intervention or the test. And this was the question I was interested in, in a woman with recurrent uterine.
Can she treat herself? And how well does that compare to a microbiological culture?
And is she correct in the diagnosis and treatment, though?
Basically, can a woman who's had a UTI before come into my surgery tell me she's got a urinary tract
infection again and I feel certain or secure that she's pretty accurate in what she's doing.
Okay. So we looked on PubMed.
Now you're all familiar with and there's a particular trial in 2001 in the Annals of Internal Medicine that actually matches our question.
There's a recurrent urinary tract infections in young women.
Patient initiated treatment of uncomplicated OC.
And here's a measurement of the accuracy of self-diagnosis determined by evidence of a definite culture,
positive or probable sterile period and no alternative diagnosis.
Okay. And here's the outcome. 88 of 172 women self-diagnosed.
The total of 172 UK laboratory evaluation showed a euro pathogen in 144 cases 84%.
So if a woman comes in to see me tomorrow is had a urinary tract infection and says, I have another one, what do you think I do?
Do you think I send off a culture? You think I just relax and go?
Here you go. Here's your prescription. I believe you.
I make sure she's telling me the right story of the symptom, but in effect, she's about 85% correct.
However, the thing is, with self labelling, lots of areas where we don't know where people are very good at self labelling.
Yeah, all these other areas. But in that area I feel I have some evidence to back me up.
I've changed the way I practice in effect. Okay.
I'm going to move on now to what we call refinement of the diagnosis.
I've showed you areas where you can simply jump in and go there.
The diagnosis, chickenpox, shingles, urinary tract infection.
There are quite a lot of them. But some areas what we end up with is uncertainty.
We have a certain idea that there are two or three possibilities now, and what we'd like to do is to refine that to a single most likely cause.
So the second area we found is what we call refinement of that diagnosis is you set
off your hypothesis like at the beginning when we said this could be chicken pox,
measles, it could be upper respiratory tract infection, but you need a number of rules or ideas to be able to help you.
And these four, five rules we came apart particularly one is that all strategies are wanting to restrict the rule to is a stepwise refinement.
The third is probabilistic reasoning and so forth with pattern recognition.
Fit on the 50. The clinical prediction now. I'm going to explain some of these, how we use them and how we might use them.
Okay. Restricted rule out. This is very interesting. This is new to me in the last two years.
Is it a learned diagnostic strategy for each presentation?
And there's a particular guy down the bottom here called John Murtagh from Australia who wrote a whole book about this.
It's about common problems and a safe diagnostic strategy.
And what you do is you try and find out what the common causes of the disease.
And also what you're really interested in is what's going to kill you or cause you real harm.
So, for instance, in a headache, it's very difficult in a headache to jump in and say there's a single core.
But what you would do is to check for particular common causes, migraine tension type headache.
But you also want to rule out the the other causes high blood pressure, temporal arthritis and subarachnoid haemorrhage.
And in fact, Amanda talked to me the other day about your dad or his good friend and his temporal doctor and his headache and the pulsatile vein.
And a restricted rule would have allowed you to pick that up because although
you'd have got into the Common Core and remember at the beginning I said in you,
we make mistakes, we look at things, and we go in and we jump in and we say, this is a migraine, but rules.
And there are a number of these that can be applied. When you've got serious issues, you have to stop and think of the one or two causes.
Prediction role. Okay. This is an interesting one.
Prediction. Which ones do you use in practice? How many people who use a prediction rule?
To people at the back. I'm going to exclude them because I know that I might use this one.
Might urine three. Okay. Okay.
Clinical prediction rules are like at the beginning when I did with the car, we're an attempt to put measurement in some way to help with what we do.
There are a number of the GP's used. When we did this ultra uncool streptococcal full throat rule ABCD school for
stroke risk had school for depression well rule for DVT and chest infection.
Now this is slightly skewed population because all these are academic GPAs.
So when you get a bunch of academic GP's together in a university department, you can get to about six prediction rules that are helpful.
So it's not surprising when you're in a non-academic setting. But the number is often zero.
But some of you may have heard of some of these. In your mind, you might have heard of things like the auto rental world.
So the auto rentals that will take you, for instance, can you predict which patients have an ankle fracture?
You can use clinical queries here again. In fact, I went into the systematic review here for ankle and rule.
And before their BMJ systematic review the accuracy of of proof to exclude fractures of the ankle and midfoot.
Systematic Review. There's a 22nd search for you.
Okay. That's how useful clinical queries can be.
You can look for systematic reviews in diagnosing. Okay.
Let's go to Uncle Ruth. I put this up in an emergency department where they all said they'd heard of the old one call rules.
I did what we did now, and I did that. Okay. I removed it from the speech, and I asked people to say, tell me, what is your uncle rule?
This is what worried me now. Not one single person in the room.
This is about 25 people could actually tell me the rule or the same variant of the rule.
So we have these things that are incredibly helpful and I'll show you how helpful they are.
But we have no strategy and have not worked out any way how to get them into practice.
And all we ever get is how do we change practice at the back here? Do you see the problem?
We've got simple things that will help us really well, and they're being ignored.
We don't need to have fancy change. However, we need to develop this from the bottom up.
You need to go back to your own practices, and if you did one thing, you could say, well, which room would help us in our practice?
But let's look at how helpful the outward ankle rule with this instrument has a sensitivity of almost 100% and a modest specificity,
and its use should reduce the number of unnecessary radiographs by 40% 30 to 40%.
So if you apply that rule, you actually say there's a lot of money and a lot of hassle for patients.
However, a GP is pretty smart in our place called Peter Roth.
What he does is he actually keeps about these on his desk in a little car and he pulls
out the wheels when he needs it and he pulls out the picture of this when you need it.
Because if you get it wrong, you don't get the benefits you'd expect.
So you could go back and you can look at this in any setting and determine which prediction rules might help you.
But here's the problem. Now, if this goes out live, I might get in trouble with the if it went out on the net.
But essential evidence plus is out there for sale.
Some people of you might have bought this info point book and I was looking at this is a particular chap in our department called Matthew Thompson,
who is reviewing it at the moment for us. And I don't know if you can see that just at the top, just there.
How many? This is a clinical prediction rules that are 291 of these prediction rules in the essential evidence plus.
You think that's a lot? Maybe not a lot of you.
Not for a lot. What do people think? So I've given you 300, probably overwhelms you in some way.
We haven't worked out of them, which would be useful.
People have actually sat in their setting and said, Well, which ones do we think would help us in our practice?
And just supplying free prediction rules is a waste of time.
Any instrument that just froze them in your face is a waste of time because it's too many.
And you haven't looked at the evidence and looked at your patient population and how it might help you and how it might affect how you practice.
So just giving you a top down approach is a waste of time and prediction.
You need to do it from the bottom up. Okay.
I particularly like this one. This was the bit where we talked about pattern recognition.
This was in the BMJ. Actually, I pointed out the BMJ, a 49 year old with severe flare up of ulcerative colitis,
gets admitted to a hospital and she receives intravenous hydrocortisone.
Amino salicylate and cyclosporine treatment because she's pretty and well and all that was started.
And after seven days she was then given oral prednisolone at about 60 milligrams per day.
And every day after that she started to write this note to the junior doctor.
Every time you turn off, we get this pitch, this card. Day seven, day eight, day nine, day ten.
What for? Diagnosis mania. And what's causing the mania.
Steroids. Do I need to have probabilistic reasoning or likelihood ratios now that the pattern recognition fit?
She's gone manic. She's gone psychotic, if you like, on a background of too many steroids.
There's a pattern recognition that, okay, so we build in the number of different strategies that you can employ and think about and teach about.
You don't need to know a two by two table. You don't need a calculation.
You just need to know that these sort of patterns exist and they're helpful.
You won't see a lot. Okay.
This is the panacea, I guess, of all evidence based practice.
And this is about five years ago, and this is the only bit of what people used to teach.
Okay? He used to teach what's called probabilistic reasoning in a two by two box and it's in you.
And it used to be if people could grind their way through this two by two box and understand this,
then, boy, they want one of you in the room would stand up at the end and think, I am an IBM God.
But most of us would go, Oh my God, what's this going to help us in practice?
However, we're going to have a bit of fun for about ten, 15 minutes if you want to keep going.
Nobody fell asleep yet. That's good. We can have ten or 15 minutes where we're going to.
Really? I'm going to really test you. I'm going to ask you to just think.
And if you can get these one or two principals on board, actually, you'll be far superior than most people out there in the health professional.
But before I do that, I'm just going to give you a 20/32 break so you can get yourself ready to concentrate again,
so you can have 30 seconds just to talk with your partner, and then I'm going to start again.
I want you to get better now.
I need you down in a minute. Okay.
Good. 30 seconds gone. We've got a lot to achieve.
Okay. You've all seen this wonderful graph and this is the graph.
And you can you can. It's in your book. So I'm not going to go I'm just going to talk to you about a couple of bits.
I've got this extra hour in there called Reproducible. This is not in the workbook.
I want it in the next edition of the workbook Pull because it's a lot of fun.
And here's something that you can all try out when you get back to your workplace.
Okay. When we normally do this, have a lot of fun.
When I'm in a big arena with lots of tables and I get you to all do this on each other and you can try this out when you get back.
I get three or four students and I get you to measure one head. However, the problem is a bit confined and I can't get you all to do this.
However I'd like. Mike, can you just come down?
Might from it. Can you just illustrate the principle here for me?
So what we do normally is in a big setting, in an open plan, I get three or four, even if I can imagine one head and just not tell him the result.
So I, I might just imagine my whole life is yeah, I know.
Just the head job.
You take a few inches off like usual. Oh you. Oh, dear.
That's changed. Okay. How about 59.5?
Okay. 59.5 centre. Thanks, Mike. Give Mike a round of applause.
Okay. Some of you may notice that coffee time I came around asking people to give me their measurement of my head.
Okay. And I did this.
What I called Amanda gave me this idea this morning. It was fantastic.
One of the potters. I won't share the Potters, but I thought, okay, I coffee time.
I'm going to do my own study. What I'm going to do is I'm going to take my tape measure.
And that's why I started with mine. And I'm going to take the tape, measure enough people to measure my head circumference,
and I'm going to stop doing that when somebody gets the same phone answer.
Okay. So if you do 59.5, then did you if the next person had got 59.5, I would have stopped.
And how many people do you think it would take before I got the same measurement?
Within exactly the same measurement. Well, people were measured at 201.5, although doing it 12 1225.
Right. Okay. Let's look at the look how we did.
Okay, Mike, you're out again. Mike got 59 centimetres and I went to Etna.
I'm not sure if I spelled that right, but I did. I did some odd.
She went in two inches 23 and a half inches.
So I didn't do the conversion factor there, but I was already in total.
Okay, pull that went to 60.5 centimetres.
So we went up. Okay. And Julie then went 63 centimetres.
Mike had said at the beginning, didn't he? Are we doing that? He said to me, We're doing this because your head's getting bigger.
Have to prove mine. However, Katherine said something very important to me.
She said, Does it matter where I measure it? I'm going to let you think about that yourself.
Actually, my head size went down at that point. 61 nine.
Okay, then bang. He said to me, What is happening with your head?
59.5. Does anybody know what's happening with my head?
Because according to me, it gets bigger and smaller after a cup of coffee.
Okay, Amanda, 61.5. Now, Amanda had seen these measurements because I said this is what I'm doing.
So she turned it over to the inches and said, Well, I'll just do it inches and then convert it back.
Still no help. Claire. Claire at the back there, 60 centimetres.
So I'm up to number eight person, I think. And Jean, I'm not going to get back to my group now.
And luckily down there came in at 59.5, which is the same as bang, bang.
Peter. I don't want to confuse my group anymore.
Important principle. Do you see that about measurements? Very important.
There are some nice statements there. People are asking, do you want to send me to the trenches?
Does it matter where I measure it? What is actually happening with my head?
You know, they used to use a tape measure in children when they had meningitis and it got up by seven millimetres.
Then they'd ordered an urgent three CT scan. I'm not sure what they'd order on me.
However, a tape measure I got taught to use this in obstetric practice.
It varies by up to five centimetre. In fact,
a friend of mine this happened to who actually ended up with this situation and said you
need a scan because I'm concerned that your baby is undersized by five centimetres.
However, the scan was not available for one week. Do you think she felt bad and anxious in that period?
You know, I think it's a it's a slight scandal that we do these things and then don't realise the consequences of what we've got to offer next.
So if you teach people to measure and to do it this way, yes, we try and standardise it,
but we should use these measurements to then say, what's our next action?
How do we remember at the beginning about the cost, the problems we face?
And so you often see this measure, which is not the measure in these tests, is about measure of agreement.
How well do we agree? And at the bottom, you get this cap of value, bit like very good agreement.
We can look at an x ray all the time and agree on what it failed at the top.
0.2 we get the poor agreement and generally you look in this, but that's what you've just done.
I think you'd agree that the nine people would probably be somewhere quite high up there in terms of agreement.
So would we say that using a tape measure is a useful way of measuring the head circumference?
Okay, so we wouldn't even move forward and that's an important defence.
O. O Is the significance of the difference?
Okay. Good point. Exactly. So in children it makes a difference.
I think we showed my head could vary by about five centimetres. It's about the same as what happens with the following.
And it's significant because it changes what you do next. You see that?
And even if you same person come back to the same measurement, 2 hours later something different happened.
So it's even standardising the person can have an effect on the agreement level.
Okay. But I'm going to do the last thing now.
Okay. Interpreting sensitivity and specificity. Panacea and remember is only one small strategy.
And in fact, it's only about 5% of what we do in primary care.
In hospital medicine, it's more. But there is this particular term sensitivity and specificity that probably,
as everybody heard of them to anybody not heard of them since Amanda's not heard of them.
Okay, good. Amanda, theme after class.
Okay, good. Let's do this. We're going to do this now. I'm going to speed up a bit because we're running out of time.
I think we're running out of time of about 5 minutes. Okay. I want you to spend you do this together with your partner on the side.
And I want you to just think in small groups, what is the chance this patient of having this patient has?
The disease. A disease with the prevalence of 3% must be diagnosed.
There is a test for this disease. It has a sensitivity of 50% and a specificity of 90% given a positive test.
What are the chances of the disease? Okay, I'll repeat that.
While you think it through. Somebody rings you out like my dad on the end of the phone and said he's had a PSA
test done and he's come back positive and his chances of having cancer are about 3%.
And you look up and you see that the sensitivity of this PSA test is 50%.
And the specificity of the test is 90%. Given a positive test, what are the chances of having that disease?
Now. How many people would like to. How many people feel they can just help me?
How many people feel I can really answer that question? One, two.
Okay, good. All right. Well, won't do it then. Stop. Stop.
Okay, relax. If only two people will move on. But generally, what happens is people generally answer about 50%.
The high proportion of people will at once, and maybe some of you will and for never and some of you will answer all the way.
It's quite difficult, isn't it, to do that? Very difficult to think through something about a strategy, about how you look at this problem.
But that's the information we're asking you to look at.
If you look in your books, it's going to tell you the sensitivity of this, this and the specificity of that.
And no wonder everybody finds it difficult. So don't be worried, because when you do do this, the answer is 13%.
And I'll show you doctors. With an average of 14 years expense experience answers range from 1 to 99%.
Half of them estimating the probability of 50% is about a 1% chance of a clinical person getting it right.
Okay. All right. Did you see that?
I said I want to run a few tests on you just to cover my ass.
That's the main reason people test. They don't understand. I'm going to walk you through this.
And if you want, you can ignore me now. Or you can. Look, I have the sheet for you to take back.
Just. You can use these spelling sheets to work through the thinking if you want to look at diagnosis.
What? I'm going to show you how I think. Okay.
The first thing is, what do we use a two by two table for? I don't use it for the calculations.
I use it for thinking. I think my brain is here.
Imagine if this is my brain. Okay. On the top is always disease.
Okay. On the side is always test. I never move them around.
Somebody today in our group wanted to move them around in terms of how we look at tables.
And I was like, Don't do that to me. I've been having this way around for 14 years.
I wanted to put the disease on the side. You're going to kill me. So this is an important thing in in your teaching, though.
Whichever way you teach something, keep it the same amongst all of you.
If you start to do things different ways, you'll confuse everybody.
If we teach different ways in this group, one group will start to talk to the other group and get confused.
But what I use this book for is actually for the definition.
Okay. I draw a line down and I think to myself, disease.
Going down is sensitivity.
So when I talk about sensitivity, I'm talking about the proportion of people with the disease and I'm thinking about how many of them test positive.
Do you see that? However, with the difficult thing about what I ask you is I asked you about what's called the positive predictive value.
What happens if you have a positive test and you're all lost?
But what I do is to remember the definition of sensitivity. I throw that and I just said, I gave to you.
If you've got the disease and you test positive sensitivity, that the first piece of information is to use that sensitivity.
Now, my group will know this because we spend about 2 hours on what I call natural frequency.
I think in terms of treatment effects, in terms of diagnosis, in terms of 100 people, nothing else apart from sometimes in a thousand.
But I think often the first bit of information I gave you there was a prevalence of 3% in every patient.
And I split that into actually. What does that mean in terms of 100 patients?
Three people had the disease. 97 did not.
Okay. Everybody see that? Happy with that?
Anybody not see that? Okay.
Then I gave you a piece of information. I said the sensitivity was 50%.
Which group of these people have the belief? The top bit.
How many of them? Top people who test positive? One and a half.
You see that? I'll go back. Three people had the disease.
Sensitivity, 50%. Remember them going down the column. People who have the disease.
The proportion of test positive was 50%. That's one and a half people.
Now, in effect, I could stop there because that's probably more information than anybody ever needs,
because now you can realise if you have a positive test, some people still will be left behind with the disease.
And some people will put the important feeling is to get a feeling of how these tests work in terms of of the prevalence of the disease.
Okay. We've still got these 97 people without the disease.
Okay. Now, this is the real trick. We've actually.
Set back diagnostic thinking in probabilistic reasoning many years by giving people the specificity with the sensitivity because the specificity,
if you want, you can think of the arrow and m got the arrow. It is going, Oh.
The proportion of people without the disease who test negative. But what I'm interested in is this box.
You see that? Because I wanted to go across. Now this is on.
I can't do this. It seems to be we've got this very difficult thinking that because we've got these two boxes here,
we can't mentally adjust and come up with a figure for that predictive value.
And so what's gone wrong in our wire is too difficult for us to understand.
However, what I do is I use what's called the false positive rate.
And if I go back, what I do is I do one minus the specificity immediately in my mind.
Or 100%, minus the 90%. I gave you a specificity of 90%.
You see that? And so I am interested in the false positive rate.
I'm interested in this box. The people who test positive but don't have the disease.
That is not the specificity either. I'll repeat that.
The people who test positive do not have the disease. That's what I'm interested and more interested in a positive result.
Now, when that comes out, that was 10% of 97. That's pretty easy math for me to do.
That's about ten people I do. I don't want to be exact. 9.7 is meaningless.
Okay. But what I've done is I've assembled all the people who have a positive test now.
And of them, 11 and a half, only one and a half, one and a half will have the disease that with the 15% chance.
And I repeat this point again. Well, all these patients now on this right hand side are the people who've tested positive.
But it is important to recognise that the majority of people who tested positive are these who didn't have the disease.
That's the one minus the specificity. And I think the terms of the positive tests, the specificity is of no benefit to you.
The smart people here will start to realise I'm using what's called the likelihood ratio, but I won't go there.
But what I will do is that's how I describe the result to my patient back in the natural frequency of 100.
Both of you want to have a go at this in your group.
I have these little handout sheets where you can just fill the book in, but I'll show you what it feels like.
Here's how you do it quick. You can do this and I can do this quick in my mind now.
But the most important is being in the ballpark. And I don't care if you get 15% or 10%.
What worries me is if the first three people would have got an answer, like 70% or always I start to worry.
I've changed the prevalence of the disease to 30% and the same test.
You see that same test prevalence is 30%.
This is like going from a GP setting with a probability of 3% to now in hospital.
The prevalence has gone up or the pre-test probably has gone up.
Now our previous competitor, in terms of a hundred patients, how many people have the disease?
There's 30. Okay.
Pretty happy with that. How many do not have the disease centre OC sensitivity of 50%.
Three 5050 okay.
Forget the specificity. You want the hundred percent minus the 90, which is 10%, don't you?
The false positive rate. You're interested in the proportion of people who don't have the disease who test positive.
How many people with a. 10% of. Seven and seven.
Okay, now I've just assembled you very quickly.
All the people have a positive test. 22 positive testing.
A total of 15 have the disease. The chances of you now have the disease of 70% have gone from 15 to 70%.
That's much more informative in terms of disease, in terms of thinking, in terms of what you're going to do next.
You didn't have to get it right, but you did have to be able to think mentally that you can get in the ballpark of where you're going.
I'm pleased that some of you got there.
And if you want to go back to your groups, when you look at this piece in your family, you might not do diagnostics from here on.
That fine is quite challenging. I find it a lot of fun.
I think we have to think about how we change, how we view things. However, I'm going to finish now.
But the important thing is to recognise. I like this paper. This is a Dutch paper.
When they looked at children with serious, serious infection, very low rate,
about one less than 1% of children had serious infection from all like my daughter.
Remember I told you at the beginning about this? Well, high temperature, less than full accuracy of signs and symptoms was fairly low.
The sign, Paramount in all trees was the position statement.
Something is wrong. Just like we sat there going, I think there's something wrong.
So probabilistic reasoning is only one part of a strategy.
We've put this together and I haven't given you the whole bit, but here's all the strategies and the people who've been involved at the top.
There are people, some people who like Paul and Dan and Rafael,
and we've been collecting patients and this is going to be in the BMJ, which we're very pleased about.
We've actually got this to a point where we're going to start explaining this in a whole series of articles.
So watch out. It's about 4 to 6 weeks away from going into the BMJ, and then we're going to take each one and say,
once we describe this, we're going to take the spot diagnosis and illustrate it more.
So once that's come out, I'll put this talk up, put this talk up until that's come out.
But that'll be about six weeks ago. Okay. And I particularly like this.
I'm going to finish on this by Jeff Norman.
Jeff Norman's a very willed, eminent person on education and diagnostic reason, and I've been looking it for many years.
Diagnosis is not a matter of acquiring some kind of all inclusive reasoning strategy.
To some extent, several strategies can lead to the same diagnosis.
The recognition of the strategy should encourage the use of experience to guide our search for the correct diagnosis.
So there are more ways of getting the count. And I hope that sort of makes you feel that some of the bits you can be comfortable with and say,
Maybe I'll just improve the way we do spot diagnosis. Maybe I'll look at prediction.
Maybe I'll forget the probabilistic reasoning. Like that.
I'll stop. Thank you.