Critical Appraisal. Evidence –Based Medicine. Formulate problem Track down best evidence Appraise the evidence critically Implement results in clinical practice Evaluate performance. All published studies in reputable journals:. Have the perfect design ?
Track down best evidence
Appraise the evidence critically
Implement results in clinical practice
Have the perfect design ?
Use the most appropriate statistical analysis?
Present the results in the best way?
“A sample of patients were interviewed within the first week of their admission to hospital. 46 people were assessed, representing 15% of admissions over the study period”
All soldiers crossing the Atlantic on Ship A had active drug
All soldiers crossing the Atlantic on Ship B had placebo
“The main contribution of statisticians in medical research is not to carry out statistical analyses but to inject a bit of logic into the situation”
In a randomised controlled trial:
“Patients were allocated to either a control or intervention group using date of birth”
Date of birth ‘randomisation’
= Systematic allocation (not randomisation)
Open to bias
(proportions, means, medians, ranges, standard deviations)
Treatment A (n= 8) 25%
Treatment B (n=19) 58%
Impressive improvement in crime statistics 1983-1984
Number of reported crimes reduced by almost 50%
In 1983, a man had made nuisance phone calls to the same woman (199 times)
Each had been reported and counted separately
The man was apprehended early in 1984
Pore over data until a ‘significant’ association is found
Devise a biologically plausible hypothesis to fit the association
(for mothers or fathers)
Categories split into:
Deciding on the hypothesis to be proved and matching the data to fit the hypothesis ie. selective reporting
[Procrustes, a robber in Greek mythology, made all his victims fit the length of his bed by stretching or cutting off their legs]
In a study of adverse effects of oral contraceptives on the outcome of pregnancy
Exposure defined as OC used within 600 days before a delivery or miscarriage
Why 600 days?
Why not 365 days (ie. 1 year)?
Or 2 years? Or 18 months? Or 500 days?........
Increases in production were caused by the increased attention that workers received from management
Sir Francis Galton’s publication:
“Regression towards mediocrity in hereditary stature”
Very tall parents tend to have children who are not quite as tall, while short parents tend to have taller children