Introduction

To understand God’s thoughts we must study statistics; for these are the measure of his purpose.
(Florence Nightingale, 1820-1910)

Most psychological research involves measurement, whether from a case study of a person with multiple personalities, a naturalistic observational study of chimpanzee parental behavior in the wild, a survey study of consumer product preferences, a correlational study of the relationship between aerobic exercise and well-being, or an experimental study on the effects of mood on memory. In each case, measurement yields a set of numbers, which are the findings, or data, produced by the research study. Psychologists and other scientists summarize 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 organizing, summarizing, 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 made by science reporters, weather forecasters, television advertisers, political candidates, government officials, and other persons who may use statistics in the information or arguments they present.