Bayesian decision making in primary care – or how to stop people dying of chicken pox: Bayesian decision making in primary care – or how to stop people dying of chicken pox Trisha Greenhalgh Professor of Primary Health Care UCL


Before we start:What is primary health care?: Before we start: What is primary health care?


Hospital medicine: Hospital medicine “Distinguishing the clear message of the disease from the interfering noise of the patient as a person.” Marshall Marinker. ‘The mythology of Hilda Thompson’ In Greenhalgh T and Hurwitz H (eds) ‘Narrative Based Medicine’. London: BMJ Books, 1998


Primary health care: Primary health care “In secondary care diseases stay, but patients come and go, whereas in primary care patients stay but diseases come and go." Iona Heath ‘The mystery of general practice’. London: Nuffield Provincial Hospitals Trust, 1995


Primary health care: Primary health care “First-contact care, delivered by generalists, dependent on teamwork, which is accessible, comprehensive, co-ordinated, population-based, and activated by patient choice.” Pat Gordon and Diane Plamping ‘Extending Primary Care’. Oxford: Radcliffe, 1996


Primary health care: Primary health care “Doing simple things well, for large numbers of people, few of whom feel ill.” Julian Tudor Hart ‘A new kind of doctor’. London: Merlin Press, 1998


Case historyA patient with query chicken pox: Case history A patient with query chicken pox


A patient with chicken pox: A patient with chicken pox It was Saturday morning. I was on call from 8.30 am. I got a call from one of my partners, Dr B, at 5.45 am. He was on holiday 200 miles away but had been called on his mobile phone by Health Call. One of his patients had rung Health Call and demanded a visit by Dr B. No other doctor would do.


A patient with chicken pox: A patient with chicken pox The family had a child with chicken pox. She had been seen the day before by another partner, Dr R, who has 24 years’ experience in general practice and is also a clinical assistant in dermatology. She had said it was “definitely chicken pox” and prescribed fluids, analgesia and calamine.


A patient with chicken pox: A patient with chicken pox The child had apparently deteriorated and the parents were worried. They had decided that only Dr B would know what to do. Dr B (who was many miles away) asked me to go round immediately and examine the child. I was not yet on call and keen to go for my early morning swim before surgery. What should my next move be?


Intermission: getting by as a GP: Intermission: getting by as a GP You only need to answer three questions: Are they ill or are they not ill? If ill, can I deal with it or does someone else need to be involved? If someone else, can it wait 12 weeks or can’t it? Cecilia Gould Crouch End Surgery coffee break, July 1989


Bayesian decision-making: Bayesian decision-making Pre-test odds of disease X Post-test odds of disease X TEST Y


Bayesian decision-making: Bayesian decision-making Pre-testY odds of disease X Post-testY odds of disease X TEST Y Post-testZ odds of disease X TEST Z Parent phones up to say “I think my child has chicken pox” Dr R examines child O.5 O.97 Swab to virology O.99


Bayesian decision-making: Bayesian decision-making Assume Disease X = Patient is seriously ill


Bayesian decision-making: Bayesian decision-making Pre-testP odds of serious illness Post-testP odds of serious illness TEST P Post-testQ odds of serious illness TEST Q Parent phones up asking for visit to child with chicken pox INSERT QUESTION HERE O.0005 O.005 INSERT QUESTION HERE O.5


A patient with chicken pox: A patient with chicken pox I asked: 1. “How old is the child?” [Answer: 15]


Bayesian decision-making: Bayesian decision-making Pre-testP odds of serious illness Post-testP odds of serious illness TEST P Post-testQ odds of serious illness TEST Q Parent phones up asking for visit to child with chicken pox” How old is the child? [High risk age group] O.0005 O.005 INSERT QUESTION HERE O.5


A patient with chicken pox: A patient with chicken pox I asked: 1. “How old is the child?” 2. “Why the $#*! are you so convinced that these guys are not time wasters?”


A patient with chicken pox: A patient with chicken pox He said: “For one thing, this family have been on my list for 17 years and they’ve never asked for a visit before. For another thing, they go to the most orthodox synagogue in Golders Green.”


A patient with chicken pox: A patient with chicken pox “And there’s one more thing I don’t like about this case. It wasn’t the mother who rang, it was the father. In that family, the father never does the kids’ health.”


Probability: Probability Of calling the doctor out at night: 1 in 17 years (1 in 6205) Of using the telephone on the Sabbath: 1 in 10,000? Of father rather than mother negotiating: 1 in 100? Estimate the index of parental concern.


Bayesian decision-making: Bayesian decision-making Pre-testP odds of serious illness Post-testP odds of serious illness TEST P Post-testQ odds of serious illness TEST Q Parent phones up asking for visit to child with chicken pox” How old is the child? O.0005 O.005 How worried are the parents? O.5 How old is the child? [High risk age group]


The illness script theory: The illness script theory We start by learning detailed rules about the cause, course and treatment of diseases As we gain knowledge we convert these rules to stereotypical stories (‘scripts’) We refine our knowledge by accumulating atypical and alternative stories via experience and the oral tradition (grand rounds etc) Knowledge is stored in our memory as stories


Illness scripts: chicken pox visit: Illness scripts: chicken pox visit “My febrile child should stay indoors.” “I think my child has meningitis.” “This is the first ever illness in my first baby” “My husband has got the car and I’m at home with the 3 kids.” “My husband and I are both working and it’s not convenient to take time off.”


Illness scripts: chicken pox visit: Illness scripts: chicken pox visit “My 15 year old daughter definitely has chicken pox. I’ve seen chicken pox in my other kids and this is different. I think my daughter is going to die.” DOES NOT FIT KNOWN ILLNESS SCRIPT


A patient with chicken pox: A patient with chicken pox I didn’t go for my swim. I didn’t even stop for a bath or breakfast. I drove straight to the house, where all the lights were off. The father, dressed in Orthodox Jewish style complete with long black coat and hat, came out to meet me and apologised that the lights were on a time switch which he could not override. I got a torch out of the car boot.


Slide27: There were 14 relatives in the room, lined up in silence. All the siblings had been woken up and were standing staring at me.


Narrative drama: Narrative drama Consulting room is a ‘stage’ The illness story is not told but enacted The patient’s performance is the clue to diagnosis Cheryl Mattingly. ‘Healing Dramas and Clinical Plots: The Narrative Structure of Experience’. New York: Cambridge University Press, 1998.


Slide29: On examination by torchlight, the child was conscious and co-operative, and had a typical chicken pox rash.


Slide30: She was post-pubescent and somewhat overweight. Her BP was 90/50 and pulse 100. She was possibly overbreathing (we all were). She said she couldn’t get up, or even sit up.


Slide31: On direct questioning, she said “I just don’t feel well. Maybe I’m a bit faint. No, I haven’t fainted or blacked out but it’s muzzy and I feel quite scared that something’s wrong.”


Slide32: I examined her respiratory system. She had a respiratory rate of 20 and no focal signs. That was a shame because I was hoping there would be.


Slide33: I found no other physical signs. So I decided to lie about the chest findings. I admitted her to Coppetts Wood Hospital by blue light ambulance.


Slide34: As I left the room, the father thanked me profusely for saving his daughter’s life.


A patient with chicken pox: A patient with chicken pox We didn’t hear anything for a month, and then got a discharge summary to say the child had had chicken pox with disseminated intravascular coagulation. The child had initially been admitted to Intensive Care for 5 days. The parents had been told she was lucky to have survived


Hospital medicine: Hospital medicine “Distinguishing the clear message of the disease from the interfering noise of the patient as a person.” Marshall Marinker. ‘The mythology of Hilda Thompson’. In Greenhalgh T and Hurwitz H (eds) ‘Narrative Based Medicine’. London: BMJ Books, 1998


Primary care at the interface: Primary care at the interface “Inferring the indistinct signal of serious disease from the complex, fuzzy and largely unclassifiable ‘noise’ made by the patient and the family in their cultural setting.” Trish Greenhalgh RFH Grand Round, January 2003


A note on stories: A note on stories "Neither biology nor information science has improved upon the story as a means of ordering and storing the experience of human and clinical complexity. Neither is it likely to." Kathryn Montgomery Hunter ‘Doctors' stories - the narrative structure of medical knowledge’. Princeton: Princeton University Press, 1991


A note on stories: A note on stories Story = Actors + Setting + Plot + Trouble + Surprise Kenneth Burke 1945 “A grammar of motive” [after Aristotle 528]


A note on stories: A note on stories Medical students learn to “take a history” – i.e. to distort and sanitise the illness narrative to fit a standardised formula. B and M-J Good. ‘Fiction and historicity in doctors’ stories’. In Mattingly C and Garro L. ‘Narrative and the cultural construction of illness and healing.’ Berkeley: University of California Press, 2000


Conclusion: Stories and Bayes: Conclusion: Stories and Bayes GPs may be alert to subtle aspects of the patient’s narrative (including the enacted drama of the acute illness). These hunches, which draw on personalised and contextualised tacit knowledge about the patient, and the accumulated ‘illness scripts’ of professional experience, can be articulated through dialogue Hospital doctors who don’t take the hunches of experienced GPs as “evidence” may be missing a trick


PS: The fascinoma paradox: PS: The fascinoma paradox Doctors learn to manage common problems by discussing uncommon ones “When you hear hoofbeats, don’t think zebras” Kathryn Montgomery Hunter. “Don’t think zebras”: uncertainty, interpretation, and the place of paradox in clinical education. Theoretical Medicine 1996; 17: 225-241


Case 2:A patient with depression: Case 2: A patient with depression


A story from general practice: A story from general practice TG – a locum GP Mrs Christine Morgan – a bank clerk


ACT ONE: ACT ONE


THE LETTERS: THE LETTERS


Slide56: Dear Trudy Thanks for seeing this 54 year old lady with depression. She has recently been through a divorce and is losing the family home. She has had some suicidal ideation but denies concrete plans. She works as a bank clerk but is currently off sick. She has one daughter who lives locally but with whom she has little contact, and a four year old grandson. She has been prescribed Prozac but I wonder if she is taking it. Thanks for seeing her with a view to counselling. I have also referred her to Prescription for Exercise.


Slide57: Dear Ali Thanks for seeing this 54 year old lady with depression and mild obesity. She went through a divorce recently and now feels the time has come to work on her physical shape and meet new people. She has no physical contra-indications except the usual low cardiorespiratory fitness. She is taking HRT and an antidepressant. Her blood pressure is normal. She is off sick right now but when she returns to work she will need to fit the sessions in around her flexi-time. I’m grateful to you for organising this.


ACT TWO(3 weeks later): ACT TWO (3 weeks later)


‘Textbook’ medical consultation: ‘Textbook’ medical consultation Take a history Examine the patient Order investigations Establish a differential diagnosis Prescribe treatment Refer if indicated


The narrative approach: The narrative approach Takes a holistic view of the problem Sees illness as part of a life story Places the patient as narrator [subject] Uses the storytelling (and listening) as part of the treatment The doctor’s role is partly to suggest alternative ‘storylines’


A STORYLINE HYPOTHESIS: A STORYLINE HYPOTHESIS


Slide67: ACT ONE: A fragmented, inconsistent, unfinished, unhappy story Her physical body Her marital relationship Her daughter and grandson Her friends Her work Her leisure activities ‘Dear Trudy’ letter ‘Dear Ali’ letter STORYLINE OPTION: Psychiatric illness STORYLINE OPTION: Shaping up and meeting people ACT TWO: The ‘back to work’ plot


The referral as a ‘twist in the plot’: The referral as a ‘twist in the plot’ Summarises the story so far Focuses on some aspects at the expense of others Attributes causality to events Interprets behaviour and assigns motives HENCE Changes the direction of the story


Slide69: Dear Trudy Thanks for seeing this 54 year old lady with depression. She has recently been through a divorce and is losing the family home. She has had some suicidal ideation but denies concrete plans. She works as a bank clerk but is currently off sick. She has one daughter who lives locally but with whom she has little contact, and a four year old grandson. She has been prescribed Prozac but I wonder if she is taking it. Thanks for seeing her with a view to counselling. I have also referred her to Prescription for Exercise.


Slide70: Dear Ali Thanks for seeing this 54 year old lady with depression and mild obesity. She went through a divorce recently and now feels the time has come to work on her physical shape and meet new people. She has no physical contra-indications except the usual low cardiorespiratory fitness. She is taking HRT and an antidepressant. Her blood pressure is normal. She is off sick right now but when she returns to work she will need to fit the sessions in around her flexi-time. I’m grateful to you for organising this.


Case 2: Summary: Case 2: Summary Conventional medicine draws a linear and rational sequence of history-taking, examination, investigation, provisional diagnosis, referral and treatment. An alternative view is to see the illness as an unfinished story. A referral can be a crucial ‘twist in the plot’, and may offer the patient a range of storyline options.


Thank you for your attention: Thank you for your attention Handouts available from Marcia Rigby m.rigby@pcps.ucl.ac.uk