Evidence Based Drug Therapy: What Do the Numbers Mean?
Strengths and limitations of different measures of the effects of treatments.Key Concepts addressed:
- 2-2 Comparison groups should be similar
- 2-5 People should not know which treatment they get
- 2-15 Fair comparisons with few people or outcome events can be misleading
Imagine you just discovered that you have a risk factor for cardiovascular disease (e.g. High LDL cholesterol). A drug that will reduce this risk factor is available, and it has a low incidence of side effects. Consider the 3 following scenarios. Would you be willing to take this drug daily for the next 5 years if significant results from randomised placebo controlled
trials showed that:
- Patients taking this drug for 5 years have 34% fewer heart attacks than patients taking placebo; or
- 2.7% of the patients taking this drug for 5 years had a heart attack, comparing to 4.1% taking a placebo, a difference of 1.4%; or
- if 71 patients took this drug for five years the drug would prevent one from having a heart attack. There is no way of knowing in advance which person that
Did you make the same decision for all three scenarios? If not, you were fooled by the numbers, because the three scenarios represent the same data from the
same trial presented to you in three different ways.