| Non-Ratio Scales | Ratio Scales
| Discrete | Scales In principle, this category would include any discrete equal interval scale that does not have an absolute zero point. In practice, however, it is an empty category, since any discrete equal interval scale is basically a scale for counting up the number of discrete, indivisible units of a certain type (e.g., the number of students in a classroom), and in any such enumeration it is always possible to end up with a count of absolutely zero.
| In general, any process of measurement in which you are counting up the number of discrete, indivisible items of some particular type. E.g., the number of students in a classroom, the number of behaviors of a certain kind performed by an organism during a given period of time, the number of faculty members in a department who are both males and tenured.
| Continuous | Scales In general, any continuous equal interval scale that does not have an absolute zero point. The most familiar examples are the Fahrenheit and Celsius scales for the measurement of temperature.
| In general, any continuous equal interval scale that does have an absolute zero point. Examples include virtually any standard equal interval scale for the measurement of continuous variables that you can readily call to mind (except for the Fahrenheit and Celsius temperature scales): inches, centimeters, quarts, liters, volts, amperes, degrees of angle, time in seconds, etc. This category also includes (a) all averages based on equal interval ratio scales, even if the original scale is discrete (e.g., average number of students per class), and (b) all measures of difference between continuous equal interval measures, even if the original scale is non-ratio (e.g., the difference between two measures of temperature in degrees Fahrenheit).
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