In the application of statistical treatments, two types of data are recognized:

1. Measures of Central Tendency - are averages or what is typical for a group of values such as scores, grades, etc. The three major measures of central tendency are the mean, median and mode.


2. Measures of Spread or Dispersion - are statistical measures which show contrasts or differences in a group of values. The major measures of spread are the range, deviation, variance, and standard deviation.


3. Measures of Relative Position - are conversions of values, usually standardized test scores, to show where a given value stands in relation to other values of the same grouping. The most common example is the conversion of scores on standardized tests to show where a given student stands in relation to other students of the same age, grade level, etc. Sigma scores, College Board scores, percentiles, stanines, and standard scores are examples of converted test scores.


4. Measures of Relationship - are statistical measures which show a relationship between two or more paired variables or two or more sets of data. The major statistical measure of relationship is the correlation coefficient.