Types of Measurement Variables

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1. EQUAL INTERVAL SCALE

An equal interval variable is a measurement where the difference between two values is meaningful. The difference between a temperature of 100 degrees and 90 degrees is the same difference as between 90 degrees and 80 degrees.

Interval data are always numerical, and the numbers assigned to two units can be subtracted to determine the difference between the units with respect to the variable being measured.

EXAMPLES:

The following are examples of interval data:

1. The temperature (in degrees Fahrenheit) at which each of a sample of 20 pieces of heat-resistant begins to melt.

2. The scores of a sample of 150 law school applicants on the LSAT, a standardized law school entrance exam administered nationwide. For example, the difference between the numerical values assigned to the units is meaningful - the difference between scores of 600 and 580 on the LSAT is the same as that between the scores of 520 and 500.

3. The time at which the 5 P.M. Washington to New York air shuttle arrives at LaQuardia on each of a sample of 30 weekdays. For example, the difference between the numerical values assigned to the units is meaningful -the morning shuttle due at 9 A.M. but arriving 9:20 A.M. is just as late as the afternoon shuttle due at 5:30 P.M and arriving at 5:50 P.M. Note in each case that the difference is the key, not the numerical measurement itself. (1)

2. RANK ORDER

A Rank Order scale gives the respondent a set of items and asks them to put the items in some form of order.
The measure of 'order' can include such as preference, importance, liking, effectiveness and so on.

The order is often a simple ordinal structure (A is higher than B). It can also be done by relative position (A scores 10 whilst B scores 6).

EXAMPLE:

Please write a letter next to the four evening activities below to show your preference. Use A for your most preferred activity, B for the next preferred, then C for the next and then D for the least preferred.
__ Staying in and watching television
__ Going bowling
__ Going out for a meal
__ Going to a bar with a friend (http://changingminds.org/explanations/research/measurement/rank_ordering.htm).

3. NOMINAL SCALE (categorical data)

Nominal data are measurements that simply classify the units of the sample (or population) into categories - often in terms of labels rather than numbers. A categorical variable, also called a ...