Biotech Values

[iwfal]

Explanation of the Chi Square example:

You have 100 patients in each arm. In the placebo arm 30 'get better' just due to the attention that they get in the trial. In a perfectly ballanced trial by definition 30 of the patients in the treated arm will do the same. In addition the treatment actually helps 10 people. Assuming that this treatment effect is uncorrelated with the placebo responders that means that in a perfectly ballanced trial (30 placebo responders in each arm) you would get 30 responders in the placebo arm and about 40 in the treated arm (really should be nearer 37, but that would just make the regression effect larger).

Now assume that you find that a certain psychological profile predicts a significant proportion (2/3) of placebo response so you regress this out. Thus you are left with 10 responses in the placebo arm and 20 in the treated. The treatment effect is unmasked.