Interval Scale

Temperature Scales and Standardized Tests

Temperature scales including the Fahrenheit and Celsius temperature scales are examples of an interval scale. For example, the Fahrenheit temperature scale in which the difference between 25° and 30° is the same as the difference between 80° and 85°. In the Celsius temperature scales, the distance between 16° and 18° is the same as that between 78° and 80°.

However, 60°F is not twice as hot as 30°F. Similarly, −40° C is not twice as cold as −20° C. This is because both Fahrenheit and Celsius temperature scales do not have a “true zero” point. The zero points in the Fahrenheit and Celsius temperature scales are arbitrary—in both scales, 0° does not mean the lack of heat nor cold.

In contrast, the Kelvin temperature scale is based on a “true zero” point. The zero point of the Kelvin temperature scale, which is equivalent to −459.67°F or −273.15°C is considered the lowest possible temperature of anything in the universe. In the Kelvin temperature scale, 400 K is twice as hot as 200 K, and 100 K is twice as cold as 200 K. The Kelvin temperature scale is not an example of interval scale but that of ratio scale.

Standardized tests, including Intelligence Quotient (IQ), Scholastic Assessment Test (SAT), Graduate Record Examination (GRE), Graduate Management Admission Test (GMAT), and Miller Analogies Test (MAT) are also examples of an interval scale. For example, in the IQ scale, the difference between 150 and 160 is the same as that between 80 and 90. Similarly, the distance in the GRE scores between 350 and 400 is the same as the distance between 500 and 550.

Standardized tests are not based on a “true zero” point that represents the lack of intelligence. These standardized tests do not even have a zero point. The lowest possible score for these standardized tests is not zero. Because of the lack of a “true zero” point, standardized tests cannot make statements about the ratio of their scores. Those who have an IQ score of 150 are not twice as intelligent as those who have an IQ score of 75. Similarly, such a ratio cannot apply to other standardized tests including SAT, GRE, GMAT, or MAT.

Likert Scales

One example of interval scale measurement that is widely used in social science is the Likert scale. In experimental research, particularly in social sciences, there are measurements to capture attitudes, perceptions, positions, feelings, thoughts, or points of view of research participants. Research participants are given questions and they are expected to express their responses by choosing one of five or seven rank-ordered response choices that is closest to their attitudes, perceptions, positions, feelings, thoughts, or points of view.

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