Clinical Epidemiology

1
Clinical Epidemiology
Using Evidence to Guide Practice
A bit of thinking and a few simple sums
2
What you need to know for the MRCGP

• Sums
• ARR, RRR, NNT (calculate) plus OR
• Impact of baseline risks
• P values, Confidence Intervals (principles, not
  how to calculate)
• Power (principles)
• Diagnosis and screening
• Sensitivity, specificity, PPV, NPV (LRs
  unlikely?)
• Concepts
• Types of studies, including SR MA, qualitative
  research (principles), health economics
  (principles)
• Where to find evidence (in the real world)
• How to use EBM in the consultation

3
Who likes shopping?(Oh no, I really hate that)
Apples were 30 a bag, now only 20 a bag.

1. Saving is 10 per bag (Original rate new rate).
2. Saving is one third or 33. (original rate new
   rate / original rate i.e. 3-2 1, 1/3 one
   third, 1/3 x 100 33

• Apples 3p a bag, now 2p a bag
• Saving is 1p a bag
• Saving is STILL one third

Would you go out and buy apples if the saving was
ONLY described as ONE THIRD OFF?
4
Describing differences between treatments

• In a RCT, 50 of people died using medicine A.
• Only 45 of people died when they were given
  medicine B.
• How much better is B than A?
• Does it matter how we describe those differences?
• What is the best way, or the fairest way, of
  describing differences?

5

• In a RCT, 50 of people died using medicine A.
  Only 45 of people died when they were given
  medicine B.
• The difference is 5.
• (Control rate experimental rate 50 - 45
  5.)
• Absolute risk reduction (ARR) or risk difference
• The difference is 10.
• Control rate experimental rate / control rate
• 50 - 45 5 / 50 1/10 10.
• Relative risk reduction (RRR) or risk ratio
• Which of these is best or fairer?

6
Same medicines, different people

• In a RCT, 5 of people died using medicine A.
  Only 4.5 of people died when they were given
  medicine B.
• The difference is 0.5.
• (Control rate experimental rate 5 - 4.5
  0.5.)
• ARR 0.5.
• The difference is 10.
• Control rate experimental rate / control rate
• 5 - 4.5 0.5 / 5 1/10 10.
• RRR 10.

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Imagine two trials
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So lets get this straight

• The RRR stays constant in different populations.
• The ARR alters in different populations it will
  be much more impressive if the population has a
  lot of events i.e. has a high baseline risk.
• But if there are not many events then a 10, 20
  or even a 30 reduction in a rare event doesnt
  amount to much benefit. And EVERYBODY has to take
  the intervention (and so is at risk of side
  effects).

9
Numbers needed to treat (NNT)

• Medicine A cures 50 of people
• Medicine B cures 60 of people
• ARR 10
• RRR 20
• Another way of looking at the absolute rate is to
  divide it into 100
• In this case 100/10 10.
• i.e. treat ten people with B rather than A and 1
  will benefit.

10
Same medicines, different people again

• In RCT 1
• 50 of people died using medicine A
• Only 45 of people died using medicine B.
• ARR 5, RRR 10, NNT 20.

• In RCT 2
• 5 of people died using medicine A.
• Only 4.5 of people died using medicine B.
• ARR 0.5. RRR 10. NNT 200.

In the higher risk population, we would only need
to treat 20 people with B rather than A to save
one.
But in the lower risk population we would need to
treat 200 people with B rather than A to save one.
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Effect of baseline risk on ARR
Event a coronary death or a non-fatal MI
4S
2
ARR
1
CARE
WOSCOPS
LIPID
ACTC
0
0
6
3
1
2
4
5
Baseline annual risk of an event
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Mini-test (1)

• Calculate the ARRs, RRRs and NNTs
  for these trials
• Medicine A 15 have an MI, Medicine B 12 have an
  MI.
• Medicine A 7 have an epileptic fit, Medicine B
  5 have an epileptic fit.
• Medicine A 12 develop diabetic retinopathy,
  Medicine B 6 develop diabetic retinopathy.
• Medicine A 27 are readmitted with heart failure,
  Medicine B, 24 are readmitted with heart failure.

13
Mini-test (1) answers

• Calculate the ARRs, RRRs and NNTs for these
  trials
• ARR RRR NNT
• 3 20 33
• 2 29 50
• 6 50 17
• 3 11 33

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Clopidogrel in ACS

• Its really beneficial Id want all of my
  patients to be taking it
• Most people do fine just on aspirin. Adding
  clopidogrel prevents only a few people having an
  event and theres the increased bleeding risk
• The specialist starts it and I dont question that

15
20 relative risk reduction 2.1 absolute risk
reduction NNT 48
38 relative risk increase 1 absolute risk
increase NNT 100
N Engl J Med 2001 345 494-502.
16

• Translation Clopidogrel significantly reduces
  the absolute risk of
• CV Death, MI, Stroke taken together by 2.1 (p lt
  0.001) NNT 48
• CV Death, MI, Stroke, and Refractory Ischaemia
  taken together by 2.3 (p lt 0.001) NNT 43
• Most benefit is achieved by 30 days with MI
• There is no effect on all cause mortality
• There is a large (relative 38) significant
  excess of major bleeds

17
This is appallingNuovo J, et al. JAMA 2002 287
2813 4.

• Ann Intern Med, BMJ, JAMA, Lancet, NEJM
• 1989, 1992, 1995, 1998.
• Treatment RCTs
• 359 eligible articles.
• NNT reported in 8 (6 of these in 1998)
• ARR reported in 18 (10 of these in 1998).
• Put another way, 93 of all RCTs only report
  relative risk.

18
Odds ratios or relative risks?Macfarlane J et
al. BMJ 2002 13 105-9
Patients who took antibiotics Patients who did not take antibiotics TOTAL
Patients who were given a leaflet 49 55 104
Patients not given a leaflet 63 38 101
TOTAL 112 93 205
19
Patients who took antibiotics Patients who did not take antibiotics TOTAL
Patients who were given a leaflet 49 55 104
Patients not given a leaflet 63 38 101
TOTAL 112 93 205
Relative risk (49/104) / (63/101) 0.76. i.e
the relative risk of patients taking an
antibiotic if they were given a leaflet is
reduced by 24. (Also called risk ratio)
20
Patients who took antibiotics Patients who did not take antibiotics TOTAL
Patients who were given a leaflet 49 55 104
Patients not given a leaflet 63 38 101
TOTAL 112 93 205
Odds ratio (49/55) / (63/38) 0.54. There was a
46 reduction in the ratio of those taking
antibiotics who had a leaflet compared with the
ratio of those taking antibiotics who did not
have a leaflet.
21
Patients who took antibiotics Patients who did not take antibiotics TOTAL
Patients who were given a leaflet 49 55 104
Patients not given a leaflet 63 38 101
TOTAL 112 93 205
Absolute risk reduction (63/101) (49/104)
0.15. Also known as the risk difference. i.e. the
difference in the risk of taking antibiotics
depending on whether a leaflet was used or not.
22
Patients who took antibiotics Patients who did not take antibiotics TOTAL
Patients who were given a leaflet 49 55 104
Patients not given a leaflet 63 38 101
TOTAL 112 93 205
NNT 1 / 0.15 7. i.e. 7 people need to be given
a leaflet In order for 1 additional person not to
take antibiotics
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What you need to know for the MRCGP

• ARR, RRR, NNT (calculate) plus OR
• Impact of baseline risks
• P values, Confidence Intervals (principles, not
  how to calculate)
• Power (principles)
• Diagnosis and screening
• Sensitivity, specificity, PPV, NPV (LRs unlikely)
• Types of studies, including SR MA, qualitative
  research (principles), health economics
  (principles)
• Where to find evidence (in the real world)
• How to use EBM in the consultation

24
matters
Size
25
How does the size of the study affect
things?Counsell CE, et al. BMJ 1994 309
1677-1681. Bandolier Nov 2002

• Investigators used a dice to simulate outcomes in
  a trial
• Treatment arm vs. control arm
• Roll of a dice outcome in the trial
• 1-5 survival
• 6 death
• Did for treatment group then repeated for
  control group
• Number of times the dice was rolled varied from 5
  to 100.

26
But its the size that matters

• Results according to number of times the dice was
  rolled
• Variation in outcome was largest in the
  smallest studies
• i.e the chance of a spurious result decreased
  with increasing numbers included in the trial

27
How good is the evidence for the management of
schizophrenia Thornley B, et al. BMJ 1998 317
1181-84
Size of trials (n1941 59 studies did not report
study size)
28
Sub-group analyses caveat emptor

• ISIS 2 trial
• 17,187 patients, 417 hospitals up to 24 hours
  after MI.
• Randomised to either streptokinase, aspirin or
  placebo in 2x2 factorial design
• Streptokinase alone and aspirin alone each
  produced a highly significant reduction in 5-week
  vascular mortality ARR 2,8, together ARR vs
  double placebo 5.2.
• To try and allay concerns re benefitsafety ratio
  in subgroups, the Lancet pushed for subgroup
  analyses.
• The authors agreed but with the proviso that
  they should analyse by astrological star signs
  and that this should appear first in the table of
  subgroup results.
• The result?

Gemini and Libra aspirin of no benefit. All
other star signs aspirin strongly beneficial
29
What you need to know for the MRCGP

• ARR, RRR, NNT (calculate) plus OR
• Impact of baseline risks
• P values, Confidence Intervals (principles, not
  how to calculate)
• Power (principles)
• Diagnosis and screening
• Sensitivity, specificity, PPV, NPV (LRs unlikely)
• Types of studies, including SR MA, and
  qualitative research (principles)
• Where to find evidence (in the real world)
• How to use EBM in the consultation

30
Plt 0.05
The Sacred P-Value

• The Shrine of
• Statistics

31
Are you happy with 1 in 20?
32
Did he just say P 0.05 ????
P 0.027 means this result occurs BY CHANCE
1 time in 36 If P 0.0001, 1 time in
10,000 by chance
33
Confidence intervals are the range of values
between which we could be 95 certain that this
result would lie if this intervention was applied
to the general population
34
Confidence Intervals Estrogen Replacement Therapy
in Women with a History of Proliferative Breast
Disease
35
Confidence intervals are the range of values
between which we could be 95 certain that this
result would lie if this intervention was applied
to the general population
Since the 95 CI crosses 1.0, the difference is
not significant
95 C.I.
1.2
0.91
0.68
Risk could be this high
Risk could be this low
1.0
36
Silverstein FE, et al. JAMA 2000 284 1247-1255

• 6 month data
  Incidence rate per year
• Celecoxib NSAIDs NNT
• All patients
• upper GI ulcer complications alone 0.76 1.45
  (P0.09) -
• combined with symptomatic ulcers 2.08 3.54
  (P0.02) 68
• For patients not taking aspirin
• upper GI ulcer complications alone 0.44 1.27
  (P 0.04) 121
• combined with symptomatic ulcers 1.40 2.91
  (P 0.02) 66
• For patients taking aspirin
• upper GI ulcer complications alone 2.01 2.12
  (P 0.92) -
• combined with symptomatic ulcers 4.70 6.00
  (P 0.49). -

37
Kaplan-Meier estimates for ulcer complications
according to traditional definitionJüni P, et
al. BMJ 2002 324 1287-1288
38
What you need to know for the MRCGP

• ARR, RRR, NNT (calculate) plus OR
• Impact of baseline risks
• P values, Confidence Intervals (principles, not
  how to calculate)
• Power (principles)
• Diagnosis and screening
• Sensitivity, specificity, PPV, NPV (LRs unlikely)
• Types of studies, including SR MA, qualitative
  research (principles), health economics
  (principles)
• Where to find evidence (in the real world)
• How to use EBM in the consultation

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B
C
No Disease
Disease
A
Percent of population
0
10
20
30
VALUE Arbitrary Units
Set cut off at A
A lot of people who do not have the disease
are labeled as having it (false positives)
A lot of people who do have the disease
are labeled as not having it (false negatives)
Set cut off at B
40
How many people in the study?
Disease
Present
Absent
Positive
Test
Negative
100
41
How many had the disease?
Disease
Present
Absent
Positive
Test
Negative
50
100
50
42
How many with the disease had a positive
test?How many without the disease had a negative
test?
Disease
Present
Absent
Positive
50
45
5
Test
50
Negative
5
45
50
50
100
43
What was the prevalence of disease in those
tested?
Disease
Present
Absent
Positive
45
5
50
Test
50
Negative
5
45
50
50
100
Prevalence 50/100 50
44
So Sensitivity and specificity
Disease
Present
Absent
Positive
50
45
5
Test
50
Negative
5
45
50
50
100
5/50 false negatives i.e. sensitivity
45/50 90
5/50 false positives i.e. specificity 45/50
90
45
Positive Predictive Value and Negative Predictive
Value
Disease
Present
Absent
PPV 45/50 90
Positive
50
45
5
Test
50
Negative
5
45
NPV 45/50 90
50
50
100
46
Watch what happens when the prevalence drops to
10NB. PLEASE remember this bit!!!!!!!
Disease
PPV 9/18 50
Present
Absent
Positive
18
9
9
Test
82
Negative
1
81
NPV 81/82 99
10
90
100
Prevalence 10/100 10
1/10 false negatives i.e. sensitivity 9/10 90
9/90 false positives i.e. specificity 81/90
90
47
H Pylori infection in a population with a 25
prevalenceMeReC Bulletin 2001 12 (1) 1-4
48
So what does all this mean?

• In primary care many people have a low chance of
  having the disease they are being tested for.
• If they get a positive test then they may have
  the disease or it could be a false positive.
  They may need more tests to sort out whether they
  truly, truly have the disease.
• (But what will the patient think when you tell
  them their initial test indicates they may have
  something and they need further tests?)
• If they get a negative test, and they are
  unlikely to have the disease, then its really
  very unlikely that they have it when they have
  tested negative.
• And MOST IMPORTANTLY, try only to test people for
  anything if they are in a high risk group for
  having the disease. Testing lots of people will
  do more harm than good.

49
What you need to know for the MRCGP

• Sums
• ARR, RRR, NNT (calculate) plus OR
• Impact of baseline risks
• P values, Confidence Intervals (principles, not
  how to calculate)
• Power (principles)
• Diagnosis and screening
• Sensitivity, specificity, PPV, NPV (LRs unlikely)
• Concepts
• Types of studies, including SR MA, qualitative
  research (principles), health economics
  (principles)
• Where to find evidence (in the real world)
• How to use EBM in the consultation

50
My brain hurts
Mr T F Gumby
51
Take a break
52
What you need to know for the MRCGP

• ARR, RRR, NNT (calculate) plus OR
• Impact of baseline risks
• P values, Confidence Intervals (principles, not
  how to calculate)
• Power (principles)
• Diagnosis and screening
• Sensitivity, specificity, PPV, NPV (LRs unlikely)
• Types of studies, including SR MA, qualitative
  research (principles), health economics
  (principles)
• Where to find evidence (in the real world)
• How to use EBM in the consultation

53
Three Steps to (primary care consultation)
Heaven
Now there are Three Steps To HeavenJust listen
and you will plainly seeAnd as life travels
onAnd things do go wrongJust follow steps one,
two and three
54
Acknowledgements

• Prof Allen Shaughnessay, Tufts University, Boston
• Prof Dave Slawson, University of Virginia,
  Charlottesville
• Prof Trisha Greenhalgh, University College,
  London

55
Step 1

• Make the best attempt at an initial (often
  provisional) diagnosis
• open questions
• clarify ideas, concerns and expectations (Can
  work in biomedical, anticipatory and hermeneutic
  relationships with patients)
• examine appropriately
• exclude red flags
• Beware of the limits of pattern recognition use
  Bayesian approaches where possible

Step one - you find a girl to love
56
Development of Medical Expertise Psychology of
Medical Decision Making Vanderbilt University.

• Stage 1. Elaborated causal networks
• Learned during the basic science years
• Facts and relationships
• Nodes and links
• Causal models of disease processes

57
Pathophysiology
Epidemiology, risk factors
Anatomy, physiology, biochemistry
Target condition
Consultation skills

• Clinical features
• Forceful features
• relevant cues

• Clinical management options
• Acute
• chronic

58

• Stage 2. Compilation of abridged networks
• Starts when exposed to real patients
• Knowledge gets compiled (rewritten, automated)
• simplified causal models
• explain signs and symptoms
• associated with diagnostic labels

59

• Stage 3. Illness Scripts.
• Based on repeated experience with patients
• Illness scripts are sufficient to diagnose and
  treat diseases.
• Lists of features that characterize the disease
• Specification of what to do
• Information about context
• Information about temporal features of disease

60

• Stage 4. Cases.
• Patient encounters stored as instance scripts.
• Based on long experience
• Physician remembers many individual patients
• Each has a different variant of the disease
• New (or newly sick) patients are
• recognized as similar to Patient X
• treated as Patient X was treated

61
Making a diagnosisElstein AS and Schwarz A. BMJ
2002 324 729732

• Problem solving
• Testing hypotheses (novices), (complex)
• Failure to generate correct hypothesis
• data collected thoroughly but ignore /
  misunderstand / misinterpret
• too economical, but interpret accurately what is
  available
• Pattern recognition (experts), (familiar)
• Mental models
• Neither are proof against error (see Klein, BMJ
  2005 330 781784)
• Decision making
• Pre test probability, LR, post test probability
  (see Gill CJ, et al. BMJ 2005 330 10801083.)
• A minority sport (consciously)

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Learn the basic patterns
64
Then can see them in new situations.
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Dwivedi G, et al. BMJ 2006 332 406

• Mrs Patel (28 years, 7 month old baby) presents
  as an emergency with a severe episode of R chest
  pain.
• Pain started 2 months ago, well localised over
  the R chest wall with no radiation. Precipitated
  by exertion, particularly by pushing daughter in
  pushchair, limits recreational activities with
  child
• Pain not exacerbated by deep inspiration,
  coughing or twisting no dyspnoea, palpitations
  or dizziness.
• Previous consultation musculoskeletal pain.
• PMH Type 2 diabetes 3 years, well controlled on
  oral medication (HbA1c 7.5) hypothryoidism,
  l-thyroxine 25micrograms daily
• Never smoked, no history of hypertension, lipid
  status unknown

67

• On examination
• Obese (BMI 34.6)
• P 70/min, regular, BP 130/70
• All peripheral pulses palpable, no bruits
• Heart sounds are normal, no murmurs
• Chest clear
• No breast lumps or tenderness
• Abdo examination normal
• Resting ECG sinus rhythm, poor R wave
  progression in anterior chest leads, inverted and
  biphasic T waves in V2 and V3.

68

• Whats the diagnosis?
• Musculoskeletal?
• Dyspepsia?
• Pulmonary embolism?
• Cholecystitis?
• Ischaemic heart disease?
• Something else?

69

• Mr Patel, 55 years, presents as an emergency with
  a severe episode of R chest pain.
• Pain started 2 months ago, well localised over
  the R chest wall with no radiation. Precipitated
  by exertion, particularly by pushing
  granddaughter in pushchair, limits recreational
  activities with child
• Pain not exacerbated by deep inspiration,
  coughing or twisting no dyspnoea, palpitations
  or dizziness.
• Previous GP consultation musculoskeletal pain.
• PMH Diabetes 3 years, well controlled on oral
  medication (HbA1c 7.5) hypothryoidism,
  l-thyroxine 25micrograms daily
• Never smoked, no history of hypertension, lipid
  status unknown

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Mrs Patel

• Seen and admitted by cardiologist
• HB 13.1, ESR 20 (slightly raised), Biochemistry
  normal
• D-Dimer normal (lt250ng/ml)
• TC 6, LDL 3.13, TG 3.47
• TFTs free T4 lt5pmol/l, TSH 151mIU/l
• Treadmill 3min51sec Bruce protocol chest
  discomfort, maximum HR 155, no ECG changes
  indicative of ischaemia
• Echo after exercise test large area of reduced
  systolic wall thickening affecting anterior
  septum and apex with obvious LV dilatation
• Angiogram critical lesion proximal LAD artery.
• Angioplasty DE stent
• Aspirin, clopidogrel and atorvastatin started,
  thyroxine dose doubled
• 6 months plus later is doing well

71
Has my neighbor won the lottery?

• Pre test probability extremely low
• Test 1 my neighbour says hes won still low
  likelihood (hes a joker) LR
• Test 2 (he says hes won and) he disappears on
  holiday for three weeks and comes back with QE2
  stickers on his luggage slightly more likely LR
• Test 3 (he says hes won, hes had an expensive
  holiday and) he pulls up in a gleaming new
  Bentley Continental more and more likely LR
• Test 4 (he says hes won, has had an expensive
  holiday and bought an expensive car and) he is no
  longer my neighbor, having bought a very big
  house in the country LR
• Test 5 (the police arrest him and charge him
  with a 50million gold bullion robbery) LR-

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How many times more (or less) likely are you to
have an MI if you develop chest pain and have
these signs / symptoms?
e.g. 1 no change in likelihood 2 twice as
likely 10 ten times more likely 0.5 half
as likely 0.1 ten time less likely etc.

• Chest pain sharp or stabbing
• Chest pain radiates to left arm
• Chest pain most important symptom
• Nausea or vomiting
• Perspiring
• BP lt 80mmHg
• Chest pain reproduced by palpation

73
Youve just estimated likelihood ratios

• The likelihood ratio is the number of times more
  or less likely it is that someone with that
  symptom has the disease
• The greater the LR, the more likely the person is
  to have the disease
• A LR more than 10 tends to rule in disease (but
  beware if the disease is very unlikely)
• The smaller the LR, the less likely person is to
  have the disease
• A LR less than 0.1 tends to rule out disease
  (but beware if the disease is very likely)

74
Likelihood ratios express how many more times (or
less times) a test result is to be found in
diseased people compared with non-diseased people.
Disease
Present
Absent
Positive
50
45
5
Test
50
Negative
5
45
50
50
100
Positive Likelihood ratio 45/50 ( 0.90)
divided by 5/50 ( 0.10). LR 9
75
Disease
Present
Absent
Positive
50
45
5
Test
50
Negative
5
45
50
50
100
Negative likelihood ratio 5/50 ( 0.10) divided
by 45/50 ( 0.90). LR- 0.11
76
You use LRs without knowing itGill CJ, et al.
BMJ 2005 330 1080-1083

• Most symptoms have LRs around 2 and LRs around
  0.5
• On their own they dont add much
• The clever bit is that you can link them together

77
Is This Patient Having a Myocardial
Infarction?Panju AA, et al. JAMA 1998 280
1256-1263
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Step 1

• Make the best attempt at an initial (often
  provisional) diagnosis
• open questions
• clarify ideas, concerns and expectations
• examine appropriately
• exclude red flags
• Beware of the limits of pattern recognition use
  Bayesian approaches where possible

Step one - you find a girl to love
81

• You have just moved to a new town and are
  looking for a GP practice for your own care and
  that of your new family. Two doctors are
  accepting patients-
• Jane completed her VTS six months ago. She
  gained the highest marks out of the 2000
  candidates when she sat her MRCGP exam and won
  the Fraser Rose medal.
• Susan completed her postgraduate training 10
  years ago. She passed her MRCGP exam at the end
  of her VT with distinction.
• Who do you choose as your doctor?

82
Systematic review the relationship between
clinical experience and quality of health
careChoudhry NK, et al. Annals of Internal
Medicine 2005 142 260273

• 32 of the 62 evaluations (52) reported decreased
  performance with increasing years in practice for
  all outcomes assessed.
• 13 (21) reported decreasing performance with
  increasing experience for some outcomes but no
  association with other assessed.
• 1 (2) reported increasing performance with
  increasing experience for all outcomes assessed.

83
Step 2

• Be aware of the evidence base in relation to the
  possible management options
• balance efficacy, safety, cost, and patient
  factors
• never always, and never never
• get used to not knowing everything and have a
  plan for finding the best answer
• check regularly on the evidence for the
  management of the conditions seen often
• be prepared to look up the evidence for the
  management of conditions not seen often

Step two she falls in love with you
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EFFECTIVE
SAFE
Benificence
Non-malfeasance
PATIENT FACTORS
COST
Justice
Patient autonomy
Barber N. BMJ 1995 310 923-925
85
High
QUALITY OF CARE
Low
SYSTEMATIC APPLICATION OF POLICY
100
0
86
Chief Medical Officer Annual Report 2005

• The way in which clinical decisions are made,
  the extent to which they depart from research
  evidence, and the extent to which they depart
  from research evidence, and the factors that
  determine compliance with best practice
  have.been extensively studied.
• Despite this, the solution to the problem of
  clinical practice variation has not been found..

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• Financial incentives
• Guidelines
• Data feedback
• Academic detailing
• Educational
• Decision support (IT)
• Audit
• Opinion leaders
• Media
• Patient mediated

89
Benefits of implementation strategiesGrimshaw J,
et al. Journal of Continuing Education in the
health professions 2004 24 S31-S37

• Changes in practitioner behaviour in the desired
  direction, were reported in 86 of the
  comparisons made.
• The median effect size overall was approximately
  10 improvement in absolute terms.

90

• "We surveyed one acute medical take in our
  hospital. In a relatively quiet take, we saw 18
  patients with a total of 44 diagnoses. The
  guidelines that the on call physician should have
  read remembered and applied correctly for those
  conditions came to 3679 pages. This number
  included only NICE, the Royal Colleges and major
  societies from the last 3 years. If it takes 2
  min to read each page, the physician on call will
  have to spend 122h reading to keep abreast of the
  guidelines" (for one 24h on-call period).
• Allen D, Harkins KJ. Lancet 2005 365 1768

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• There are 1500 pages indexed in Medline each day.
• Prof Sir JA Muir Gray
• Best Current Evidence Strategy.
• March 2006
• (So which ones will you choose to read?)

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Abstracts lie (lots)Pitkin RM, et al JAMA 1999
281 1110-1111

• Random samples from 44 articles and their
  abstracts from Annals, BMJ, Lancet, JAMA, NEJM
  (12 months from July 1996), and 44 articles CMAJ
  (15months from July 1996) were compared with the
  original articles
• 19 of abstracts contained statements that were
  inconsistent with the full article
• 11 of abstracts contained statements that were
  not present in the full article

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20 of RCTs dont report all outcomesChan A-W,
Altman DG. BMJ 2005 330 753-756

• 519 RCTs in 553 publications were examined for
  incompletely reported outcomes per trial.
  Original authors were surveyed (response rate
  69).
• 32 denied the existence of unreported outcomes
  when there was evidence to the contrary in their
  publications.
• On average, 20 of outcomes measured in RCTs were
  incompletely reported.
• These outcomes were more likely to be non
  significant (OR 2.0, 95 CI 1.6 to 2.7) for
  efficacy outcomes OR 1.9, 95 CI 1.1 to 3.5 for
  harm outcomes.

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• So you cant keep up to date by reading primary
  research in journals.
• And if you do read some primary research in
  journals, theres a decent chance what you read
  is poorly designed, poorly conducted and poorly
  reported.
• And youve only read that research not all of
  the research which may be relevant. What if
  youve just read the one aberrant study and there
  are lots of others showing results that are the
  exact opposite and you haven't seen those?

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Evidence-based treatment for my patient
Clinician reading journals
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Evidence based medicine
Recognise lack of certainty
1. Formulate question
5. Evaluate performance
2. Efficiently track down best available evidence
4. Implement changes in clinical practice
3. Critically review the validity and
usefulness of the evidence
98

• If you ask doctors, they say they need
  information about once a week. But if you debrief
  them, they raise about 2 questions for every
  three patients Covell DG et al. Ann Intern Med
  1985 103 596599
• Many potential questions are not recognised by
  general practitioners (over confidence?, failure
  to recognise uncertainty?) Barrie AR et al. BMJ
  1997 315 15121515
• Answers to most questions are not immediately
  pursued. Ely JW et al. BMJ 1999 31 358-361
• Doctors spent an average of less than 2 minutes
  pursuing an answer, and they used readily
  available print and human resources. Only two
  questions (out of over 1100) led to a formal
  literature search.

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Travel agents consultation
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• Pattern recognition, mental maps and short cuts
  are often used FOR DIAGNOSTIC DECISION MAKING
• Management decision making
• Is the same problem (lots of complex information
  to compute)
• But creating mental maps to make sense of this is
  NOT the preferred approach when there are better
  ways to keep up to date with the evidence for
  interventions

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MindlinesGabbay and le May. BMJ 2004 329
10131016

Clinicians rarely accessed, appraised, and used
explicit evidence directly from research or other
formal sources rare exceptions were where they
might consult such sources after dealing with a
case that had particularly challenged them.
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MindlinesGabbay and le May. BMJ 2004 329
10131016

• Not once was a guideline read.
• Expert computer systems were rarely used (never
  in real time).
• Instead, they relied on what we have called
  "mindlines," collectively reinforced,
  internalised tacit guidelines, which were
  informed by brief reading, but mainly by their
  interactions with each other and with opinion
  leaders, patients, and pharmaceutical
  representatives and by other sources of largely
  tacit knowledge that built on their early
  training and their own and their colleagues'
  experience.
• The clinicians, in general, would refine their
  mindlines by acquiring tacit knowledge from
  trusted sources, mainly their colleagues, in ways
  that were mediated by the organisational features
  of the practice, such as the nature and frequency
  of meetings, the practice ethos, and its
  financial and structural features, including the
  computer system.

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Reading and critical appraisal can (largely) be
replaced by using brief summaries of evidence
from trusted sources
105
Finding the best answer, first time
InfoRetriever, DrCompanion, self-assembly
Textbooks
106
Post-modern EBM skills
1. Recognise the need to check mindlines
5. Enable your patient to play a full part in
shared decision making (if they want to)
2. Find the summarised evidence
4. Translate that into terms your patient can
understand
3. Understand the language of the evidence
107
Individuals need

• Basic clin epi (how to read a summary)
• Using Evidence to Guide Practice
• Information Mastery induction
• Where to find summaries from trusted sources
• Point of Care Information Tools
• DrCompanion, InfoRetriever
• Consultation translation skills
• Local trusted colleague(s) networked
• CPD programme for COMMON conditions, unbiased,
  evidence-based, summarised, reinforced
• Programme to spread the skills required to hunt
  for answers efficiently using the above tools

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Step 3

• Reach agreement on a management plan
• present options
• where data is available, use x in 100 will
  benefit, y in 100 will be harmed (not
  percentages)
• consider supporting with visual representation
  e.g. smiley faces, CV risk charts
• if an immediate decision is not required,
  consider materials for patient self-study
• safety netting
• housekeeping

Step three you kiss and hold her tightly
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Clopidogrel in ACS

• Its really beneficial Id want all of my
  patients to be taking it
• Most people do fine just on aspirin. Adding
  clopidogrel prevents only a few people having an
  event and theres the increased bleeding risk
• The specialist starts it and I dont question that

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N Engl J Med 2001 345 494-502
111

• Absolute risk
• Relative risk
• Numbers needed to treat
• P values
• Confidence Interval

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Clopidogrel in ACS

• Its really beneficial Id want all of my
  patients to be taking it.
• Most people do fine just on aspirin. Adding
  clopidogrel prevents only a few people having an
  event and theres the increased bleeding risk.
• The specialist starts it and I dont question
  that.

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What would happen to 100 people like you who take
sleeping tablets for more than a week.
? ? ? ? ? ? ? ? ? ?
? ? ? ? ? ? ? ? ? ?
? ? ? ? ? ? ? ? ? ?
? ? ? ? ? ? ? ? ? ?
? ? ? ? ? ? ? ? ? ?
? ? ? ? ? ? ? ? ? ?
? ? ? ? ? ? ? ? ? ?
? ? ? ? ? ? ? ? ? ?
? ? ? ? ? ? ? ? ? ?
? ? ? ? ? ? ? ? ? ?
For 76 people the tablets do NOTHING, good or bad
These SEVEN people sleep better, which means they
get an extra 25 minutes sleep a night They also
wake up once less every 2 nights
These SEVENTEEN people have side effects One of
them may be serious, like a fall or car crash
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Antibiotics for bronchitisLittle P, et al. JAMA
2005 293 30293035
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Level 3-4 diagnostic skills
The New Generalist Pinwheel
Aware of diagnostic cognitive biases uses
baseline probability and decision rules
routinely
Can work in biomedical, anticipatory and
hermeneutic relationships with patients (ICE)
Finds and understands the strength and the
language of summaries of evidence from trusted
sources
Translates that evidence for patients, uses DAs
appropriately, discusses OICJ routinely
118
Back to hard core exam prep
119
Web based resourcesAn Introduction to
Information Mastery www.poems.msu.edu/InfoMastery
National Prescribing Centre www.npc.nhs.ukDru
g And Therapeutics Bulletin
www.which.net/health/dtb/main.htmlBandolier
www.ebandolier.comClinical Evidence www.clini
calevidence.orgEffective Health Care
Bulletin www.york.ac.uk/inst/crdCochrane
Collaboration www.cochrane.co.ukNational
Institute for Clinical Excellence www.nice.org.uk
United Kingdom Medicines Information www.ukmi.nh
s.ukCentre for Evidence Based Medicine www.cebm.
netInfoPOEMS www.infopoems.comCASP www.
phru.nhs.uk/casp/casp.htmNational electronic
library for health www.nelh.nhs.uk
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How to read a paper Trisha GreenhalghBMJ 1997
315 180 3 243 6
305 8
364 6 422
5 480 3
540 3
596 9 672 5
740 3www.bmj.com
Getting research findings into practice Various
authorsBMJ 1998 317 72 5
139 42
200 3 273 6
339 42
405 9 465
8www.bmj.com
NB Health economics
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Books

• Greenhalgh T How to read a paper 2nd edn London
  BMJ Books 2001
• Sackett DL, Richardson WS, Rosenberg WMC, Haynes
  RB. Evidence-based medicine how to practice and
  teach EBM. London Churchill-Livingstone, 1996.
• Muir Gray JA. Evidence-based Healthcare.
  Churchill Livingstone. 1997.

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Are you suffering from information
overload?  There are over 30,000 biomedical
journals in print.  How do you cope? Using
Evidence to Guide Practice 5 interactive modules
available via the Internet covering the
principles of EBM and the influences on
prescribing
ALL FIVE MODULES FOR ONLY 35
E-Learning Learn at a pace and time to suit you
Go to www.npc.co.uk for more details