Jeremy Howick

Centre for Evidence-Based Medicine

1. There are no hierarchies

2. EBM has always

recognized mechanisms

3. Philosophers of science have ignored

problems with the evidential role of

mechanisms

4. The fact that ‘mechanistically

sound’ hypotheses are more believable

is irrelevant.

5. The best way to improve evidence

would be to have a minimum effect size

requirement

1. There are no hierarchies: GRADE

Downgrade for:- Inconsistency- Indirectness- Imprecision- Publication bias

Upgrade for:- Large consistent effect- Dose response- Confounders only reducing size of effect

HIGHMODERATELOWVERY LOW

Step 1: Initial ranking

Step 2: upgrade/downgrade

Step 3: assign final grade

RT:HighOS:low

1. There are no hierarchies: OCEBMPICK A BOX!

randomized trial

Cohort StudyCase Series

Mechanistic reasoning

systematic review

2. EBM has always recognized a role for mechanisms

3. Proponents of mechanisms have ignore problems with mechanisms

4. Getting the contrast class right

4. Effect size

1. There are no hierarchies

2. EBM has always

recognized mechanisms

3. Philosophers of science have ignored

problems with the evidential role of

mechanisms

4. The fact that ‘mechanistically

sound’ hypotheses are more believable

is irrelevant.

5. The best way to improve evidence

would be to have a minimum effect size

requirement

Thanks again!

jeremy.howick@phc.ox.ac.uk