The range is the difference between the highest and lowest scores. The variance is the average of the squared deviations from the mean of the set of scores. And the standard deviation is the square root of the variance. Many kinds of measurements fall on a normal, or bell-shaped, curve. A certain percentage of scores fall below each point on the abscissa of the normal curve.
Percentiles identify the percentage of scores that fall below a particular score.
Correlational Statistics Correlational statistics assess the relationship between two or more sets of scores. A correlation may be positive or negative and vary from 0.00 to plus or minus 1.00. The existence of a correlation does not necessarily mean that one of the correlated variables causes changes in the other. Nor does the existence of a correlation preclude that possibility. Correlations are commonly graphed on scatter plots.