LEVELS OF MEASUREMENT

Depending upon the type of variable that you have used, the numbers in your data table may have different meanings.

CATEGORIES

If you think about the numbers used to code some of variables in many experiments and surveys, you will realize that the particular number assigned to a category conveys no numerical information. The codes just represent the categories.

ORDERED CATEGORIES

Sometimes the order of categories is significant. Think about the exciting-routine-dull variable. The responses to the question can be arranged in a meaningful order. If we arrange them in terms of decreasing excitement, then the response "Exciting" comes first, followed by the response "Routine," and finally the response "Dull." Of course, we could have arranged the responses in the other order as well (from low excitement to high excitement). In both instances, the response "Routine" falls between the other two. There is no order to those categories, but it does mean something that Routine is between Exciting and Dull.

NUMBERS

Although the codes assigned to the exciting-routine-dull variable are ordered from high to low, they convey only order; they have no other numerical meaning. Someone who was bored with life (code 3) did not differ by two "excitement units" from someone who found life exciting (code 1). Subtracting or dividing the codes makes no sense.

On the other hand, let us say that "education" is one of the variables under study. This variable is different. The numerical code assigned to each category is not merely a code. It is the highest grade completed. It is an actual number, and we can treat it as such. For example, someone with 8 years of education has twice the number of years of education as someone with 4 years. Someone with 16 years of education has 4 more years than someone with 12 years . We can add, subtract, and divide the codes and understand the results.