Most psychological research involves measurement. In each case, measurement yields a set of numbers, which are the findings, or data, produced by the research study. Psychologists summarise data, find relationships between sets of data, and determine whether experimental manipulations have had an effect on some variable of interest.

The word statistics has two meanings: (1) the field that applies mathematical techniques to the organising, summarising, and interpreting of data, and (2) the actual mathematical techniques themselves. Knowledge of statistics has many practical benefits. Even a rudimentary knowledge of statistics will make you better able to evaluate statistical claims.

http://www.mhhe.com/socscience/intro/cafe/common/stat/