I have a huge dataset of longitudinal medical records. Each record contains indications for drug and disease.
I have been able to calculate the Outcome Rate in the population given a particular drug. This is, simply 1 minus the ratio number of diseases after the number of diseases before the drug.
Unfortunately, this calculation would suggest that every drug I am interested in has a poor level of medical efficacy. It is possible that the drugs I am interested in might only work on a subset of patients, therefore, a complete population-based study is going to be very biased.
Given how many patients show a reduction in disease after taking the drug, how can I determine whether that was statistically significant or just by chance? I would like to learn a little more about how I can compare groups of those affected by the drug and those not affected.