Statistics are an essential tool for making proper judgement decisions. It is concerned with probability distribution models, testing of hypotheses, significance tests and other means of determining the correctness of deductions and the most likely outcome of decisions. Measures of central tendency include the mean, median and mode. A second important class of descriptive statistics is measures of variability described by the standard deviation. Inferential statistics estimates what a total set of measures would be like on the basis of a sample. The standard error of the mean is a statistic that indicates an estimate of the reliability of the sample mean. The t-ratio is the ratio of the expected difference in a set of scores to the obtained difference. This can also be interpreted in relation to the normal curve. The coefficient of correlation is a measure showing the relationship of measurements on one set of variables to the measurements on another set of variables. Two variables can be highly correlated without being causally connected. (DJ)