Statistical knowledge and clinical knowledge
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Statistical knowledge and clinical knowledge
J. Nummenmaa
M.D. Ph.D.
Knowledge in Medicine -Questions in Medical Epistemology
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Evidence-Based Medicine (EBM)
• Ensure availability of reliable research results for clinicians– How effective treatment?– Research done on patients– Golden standard = Randomised trial– Critical evaluation on research &
results– Quality improvement– Decreasing variation
• EBM Guidelines – Bringing evidence to practice
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What is good evidence?
Level A: Consistent Randomised Controlled Clinical Trial, cohort study, all or none (see note below), clinical decision rule validated in different populations.Level B: Consistent Retrospective Cohort, Exploratory Cohort, Ecological Study, Outcomes Research, case-control study; or extrapolations from level A studies.Level C: Case-series study or extrapolations from level B studies.Level D: Expert opinion without explicit critical appraisal, or based on physiology, bench research or first principles.
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Randomised trial• Dr. James Lind 1747
– Scurvy prevention
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IS TREATMENT X MORE EFFECTIVE THAN Y IN THE TREATMENT OF DISEASE Z?
N PATIENTS WITH Z
HALF TREATED WITH X
HALF TREATED WITH Y
NUMBER OF END –POINTS IN DIFFERENT GROUPS
DIAGNOSIS AS CLASSIFICATIONONE DIAGNOSIS DOES NOT EXCLUDE ANOTHERDIFFERENT DIAGNOSES ARE BASED ON DIFFERENT CRITERIA
DIAGNOSTIC DIFFERENCESIN HOSPITALS AND PRIMARY CAREINTERNATIONAL
PREVALENCE AND INCIDENCEIN HOSPITALS AND PRIMARY CARE
Randomised trial
HOW TO CHOOSE WHAT
TREATMENTS ARE COMPARED?
•WHOSE CHOICE?•INDUSTRY?•WHO ELSE, UNIVERSITY?
•WHY?•FINANCIAL INTERESTS?•SCIENTIFIC INTERESTS?
•COMPARING DIFFERENT TREATMENTS•MEDICATION•SURGERY•(PSYCHO)THERAPY
•CHOOSING ONE TREATMENT = NOT CHOOSING SOME OTHER TREATMENT
PROBLEMS OF DIAGNOSTIC
CRITERIA
PROBLEMS ON PATIENT
SELECTION
•REPRESENTATIVE PATIENTS?•RANDOMISATION•BLINDING•CO-MORBIDITY•OTHER FACTORS, LIFE-STYLE ETC
ADHERENCE
SELECTION OF END-POINTS
•PREVENTION OR TREATMENT?•OBJECTIVES?
•DO ALL PATIENTS SHARE SAME OBJECTIVES•COMPOSITE INDICATORS
•APPLICABILITY ON INDIVIDUAL PATIENTS?•SIDE-EFFECTS
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Clinical importanceTreating individual patients
Clinical significance:Relative risk reduction :percentageAbsolute risk reduction (ARR%)Number needed to treat (NNT)
Significance of the data
• Statistical significance: p-value
– Propability to get achieved results if null-hypothesis is true
Statistical significance: p=0.036
Risk reduction 30.3%Out of one hundred patients:-> 97 remain healthy-> will get sick whether treated or not-> one incidence can be prevented-> ARR 1% -> NNT= 100
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Clinically significant risk?
• Cholesterol-lowering medication should
be started if a person, even otherwise
healthy, has a propability of cardiac
death higher than 5% / 10 years
– Finnish evidence based (Käypä hoito -)
guidelines for hyperlipidaemia
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To treat or not to treat?
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To treat or not to treat?
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What to do with myself?• At the age of 44• Estimated life-span 88,48• Intervention: regular exercise + 2-3
doses of alcohol • Benefits:
– 0,29 years= 1 600 hours awake– January - March– One hour / day= 16 235 hours– Costs:
• Wine 32 500 €• Exercise 500 € p.a. = 22 500 €• Total 55 000 €
– One extra hour of life= 10 hours 34€10
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Evidence-Based or Value-Based?
• Comparison of hypertension control
between different countries: 17,5 - 86,4%• Fahey & Peters: What constitutes controlled hypertension? Patient based
comparison of hypertension guidelines, BMJ, 1996, 313, 7049, 93-96
Recommendations based on same
evidence: 50% / 50%• Raine, R & al. Lancet, 2004, 364, 9432, 429-437
• Selection of literature• Christiaens & al. Scand J Prim Health Care, 2004, 22, 141-145
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Evidence-Based or Value-Based?
• 76% of Norwegian men in
Trondelage have higher risk for
cardiac diseases than guidelines
recommend
– Cholesterol
– Blood pressure
• How to deal with risks?
– Getz & al 2004
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Evidence-Based – really?• Is data really reliable?• Are the results applicable in practice?• Are the results politically acceptable?• How do the results relate to functioning of the
working group?• Moreira T (2004): Diversity in clinical guidelines: The role of repertoires
of evaluation. Soc Sci Med 60:1975-1985.
• Value-Based recommendations:– Selection of literature?– Valuation of research methodology?– How effective treatment is effective?– What treatments are favored (Drugs, surgery, therapy)?
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Hume and EBM Guidelines
• ”…when all of a sudden I am surprised to find, that instead of the usual copulations of propositions, is, and is not, I meet with no proposition that is not connected with an ought, or an ought not. This change is imperceptible; but is however, of the last consequence.”– David Hume: A treatise of human
nature (1739)14
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General Practitioner
• Treating human beings
not diseases
• Contextuality.
• Networking
• Place of treatment:
Clinic, home
• Understanding meanings
• Resource control
•Continuity•Openness•Tolerance and ability to deal with uncertainty•Clinical encounter•Social medicine•Unselected population•Patients present with symptoms
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EBM vs GP
• EBM
– Diagnosis
– Randomised trial
– Interpretation
statistical
– ”Objective”
– Uncertainty:
• Statistical
significance
• Clinical
significance
• GP
– Patient, symptom
– Individual
interpretation
– subjetive
– Uncertainty
• Limited data
• Lack of knowledge
• Applying knowledge
• Ethics & values
• Limited time
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Clinically relevant research?
• University?
• Evidence-Based Guidelines?
– Does not produce new data
– Valuation of research results
favours medical treatment
• Drug industry?
• GPs themselves?
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How does a GP use EBM Guidelines
• Source of information, as a textbook
• Searching answers for a specific question
• As an institutional quality improvement
tool– Grimshaw ja Eccles in Ridsdale L. (Ed.): Evidence-based
practice in primary care (Churchill Livingstone).