The risk determined from PMS studies

Abstract

In animal studies or in controlled clinical trials, investigators are looking for common beneficial or adverse outcomes. With these studies there is a relatively small number of factors which are likely to change at any one time. Mostly these are known and can be measured. Moreover, in most instances the time scales between first exposure and termination of the experiment are short, thus minimizing the period during which intervening variables can exercise a major effect on the study outcome. Indeed when we look at examples of trials in which there is a long delay between entry and end-point, we often find ourselves in areas of major controversy as regards the interpretations of the data - a situation not entirely dissimilar to that pertaining to most observational studies to date.