Which of the following is an example of a categorical variable?

A categorical variable is one that represents categories or groups rather than numerical values. In this context, choosing "declared major in college" reflects the nature of a categorical variable because it classifies individuals into distinct groups based on their chosen area of study, such as psychology, biology, or engineering. Each major stands as a category without implying a ranking or numerical value, making it a quintessential example of a categorical variable.

The other options, while important in their own right, represent quantitative data. For instance, height, test scores, and weight are all measured on a numerical scale and can take on a wide range of values, meaning they are quantitative variables rather than categorical. These numerical values can be averaged, compared, or subjected to various statistical analyses, which is not applicable to categorical data.