When is a variable categorical

Categorical variables are those that provide groupings that may have no logical order, or a logical order with inconsistent differences between groups e. Quantitative variables have numerical values with consistent intervals. A team of medical researchers weigh participants in kilograms. Weight in kilograms is a quantitative variable because it takes on numerical values with meaningful magnitudes and equal intervals.

A teacher conducts a poll in her class. She asks her students if they would prefer chocolate, vanilla, or strawberry ice cream at their class party. Preferred ice cream flavor is a categorical variable because the different flavors are categories with no meaningful order of magnitudes.

A census asks every household in a city how many children under the age of 18 reside there. Number of children in a household is a quantitative variable because it has a numerical value with a meaningful order and equal intervals. When a car breaks down on the highway, the emergency dispatcher may ask for the nearest mile marker. For example, suppose you have a variable, economic status, with three categories low, medium and high. In addition to being able to classify people into these three categories, you can order the categories as low, medium and high.

Now consider a variable like educational experience with values such as elementary school graduate, high school graduate, some college and college graduate. These also can be ordered as elementary school, high school, some college, and college graduate. Even though we can order these from lowest to highest, the spacing between the values may not be the same across the levels of the variables. Say we assign scores 1, 2, 3 and 4 to these four levels of educational experience and we compare the difference in education between categories one and two with the difference in educational experience between categories two and three, or the difference between categories three and four.

The difference between categories one and two elementary and high school is probably much bigger than the difference between categories two and three high school and some college. In this example, we can order the people in level of educational experience but the size of the difference between categories is inconsistent because the spacing between categories one and two is bigger than categories two and three.

If these categories were equally spaced, then the variable would be an interval variable. An interval variable is similar to an ordinal variable, except that the intervals between the values of the numerical variable are equally spaced. Statistical computations and analyses assume that the variables have a specific levels of measurement.

For example, it would not make sense to compute an average hair color. An average of a nominal variable does not make much sense because there is no intrinsic ordering of the levels of the categories.

In this study, researchers wanted to identify variables connected to low birth weights. In this example, the individuals are the patients the mothers. There are six variables in this dataset:. Consumer Reports analyzed a dataset of 77 breakfast cereals. Here is a part of the dataset. Note: Consumer Reports is an non-profit organization that rates products in an effort to help consumers make informed decisions. Privacy Policy.