Statistics for clinicians. 1. Introduction.

Statistics is a way of thinking about variable events. The relative frequency with which an event occurs is called its probability (P). By convention, events with a probability of 5% or less (P less than = 0.05) are considered rare or "significant". Data may be of nominal (categories), ordinal (grades), or interval/ratio type (measurements). Statistical methods are helpful for: summarizing data; making estimates for populations; defining "normal" range; testing association between attributes; measuring correlation between variables; computing one variable in terms of others; and testing the significance of differences between groups.