[Risk and prevention in cardiovascular diseases].

The RCTs are the most important sources of drug therapy related scientific evidence (RCT--Randomised Controlled clinical Trials). In most cases RCTs studying identical or similar clinical issues are slightly or considerably varied. However, for such cases we have the appropriate methodology to compare the more or less different RCT results. This publication was written to provide a general overview of this methodology such as relative and absolute risk reduction (RRR, ARR), odd ratio (OR), number needed to treat and number needed to harm (NNT, NNH).