Lecture Evidence based medicine: Effectiveness of therapy

This lecture includes these contents: Effectiveness of therapy, critically appraising a therapy paper, efficacy versus effectiveness, observation versus experimental studies,... Invite you to consult this lecture.

MEDICINE

Effectiveness of therapy

Ross Lawrenson

paper

paper ­ methodology

• When critically appraising a paper ask yourself three questions:

considering.

randomised?

Efficacy versus effectiveness

• Efficacy ­ does receiving treatment work under ideal conditions?

• Efficacy ­ does receiving treatment work under ideal conditions?

• Effectiveness ­ does offering treatment help under ordinary circumstances?

Observation versus  experimental studies.

studies

• A study population of 2000 patients  with acute coronary heart disease of  whom half receive a certain 

intervention and the other half do 

not. Of the 2000 patients, 700 have  arrhythmia "X" and 1300 do not.

studies

• A study population of 2000 patients with  acute coronaries of whom half receive a  certain intervention and the other half do  not. Of the 2000 patients, 700 have 

Intervention No interventionX(­)

800

X(+) 200

X(­)

500 X(+)500

Relative risk = 0.6 

Intervention No intervention X(­)

650

X(+) 350

X(­)

650 X(+)350

Relative risk = 1

•  Incidence rate of the outcome in the population (can be the treated or the untreated population)

• Relative risk  (RR) is the absolute risk 

in the treated group divided by the 

absolute risk in the untreated group (or vice versa)

• Because the randomised trial removes selection  bias the result of the study should be believed  over the evidence from the observational study  i.e. the  Relative risk is 1 (no difference in 

treatment) not 0.6 (which suggested a benefit 

from treatment.)

•  An example of this would be the use of HRT  and the reduction in cardiovascular risk. 

Observational studies have shown a 50% 

reduction in CHD but the RCT showed no 

benefit. (References)

3. Were all patients who entered  the trial properly accounted for  and attributed at its conclusion?

          Selection bias

Randomised controlled trials

Outcomes Outcomes

Sample Population

Treatment 1 Treatment 2 

(a) Selection of study population

sample

Non random sample is selected. 

e.g. Volunteers. Healthy worker. 

Hospital patients.

(b) Intention to treat analysis.