Statistical analysis in clinical laboratory medicine: fundamentals and common uses

Medical research studies may be classified into two broad categories: descriptive and inferential. Descriptive studies are intended to describe the characteristics of only the study group, using observations obtained from every member of the group. Inferential studies, on the other hand, are designed to enable the investigator to use observations from selected individuals (a sample) to make conclusions about the larger group (population) from which they were drawn. The first part of this paper deals with descriptive studies, focusing on summary statistics and graphic techniques. The remainder deals with inferential studies. We start by describing how characteristics of the population may be estimated from characteristics of a small number of its members, which are randomly selected. These principles are then applied to the problem of testing hypotheses about the population by use of some of the more common testing procedures. These include t tests, regression, chi-square tests, evaluating a new diagnostic procedure, estimating normal values, survivorship studies, and sequential methods.