Another very important component is the DATA. Data come in various types. They are a representation of reality, and show the results of measuring properties or processes.

Data and the ways they are measured come in various types. One of the most accepted typologies is Stevens' Scales of Measurement. It divides data into four types:

Nominal means "name bearing." The nominal scale places things into named categories. These things are assigned to groups according to their common or shared elements. For example women who are different in many ways could be assigned to the same category based on their shared gender. Important: The different categories are not ordered in any "more or less" sense. They are just different from each other.

The ordinal scale places things in order. Ordinal data show a particular item's position relative to other items, such as "First, second, third, etc." The ordinal scale doesn't specify the distance between each item. It just puts them in order. For example, in a playground foot race where no one has a watch, the participants will not know their actual times. They will only know who came in first, second, or third.

The interval scale uses equal-sized units of measurement (points, minutes, etc.) and, therefore, shows the distances, or intervals, between subjects' performances. In the foot race example, if the runners' classmates started counting aloud after the first runner crossed the finish line, they might discover that the second place finisher was only two counts behind the winner while the third-place finisher was ten counts behind. Interval data show this difference in distances. Ordinal data would not. It is important to remember that with interval (as opposed to ratio) data, the intervals start from an arbitrary point, not absolute zero. Therefore, a student who scores a 60 on a grammar test could not be said to know twice as much grammar as a student who scored 30. Also, the person who scored a 0 on this test would not be said to know no grammar at all.

The ratio scale is like the interval scale. It employs equal intervals. However, the ratio scale begins at a true zero point. That point represents an absolute lack of the quality being measured. Because of this characteristic, additional mathematical functions are possible with ratio data that are not possible with other types of data.

Usage note: Strictly speaking, the word data is actually a plural. The singular form (which is rarely used) is datum. Therefore, it is correct to say, for instance, "The data show" or "The data are" rather than "The data shows" or "The data is".