On a Survey, Age Was Divided into Three Categories: Younger

Multiple Choice

On a survey, age was divided into three categories: younger than 18 years, 18 to 21 years, and older than 21 years. The researcher computed the mean age of the respondents by adding up the scores and then dividing by the number of cases. Why was this a mistake?

A) because the data are interval-ratio and should not be treated as ordinal
B) because the data are only nominal and should not be treated as ordinal
C) because the data are continuous and should not be treated as discrete
D) because the data are ordinal and should not be treated as interval-ratio data