Nursing Professional Development Certification (NPD-BC) Practice Exam

For which of the following types of measurement data is there no measure of variability?

1. Nominal

2. Ordinal

3. Interval

4. Ratio

The correct answer is: Nominal

Nominal data represents categories without any inherent order or ranking. Since nominal measurements consist solely of distinct categories, such as gender, ethnicity, or the presence or absence of a characteristic, there is no meaningful way to calculate variability within these categories. Measures of variability, like range or standard deviation, require a sense of order or numerical value to assess differences across a dataset. In contrast, ordinal data has a clear order but does not specify the exact differences between ranks; interval and ratio data not only have an order but also provide a basis for calculating variability since they involve numerical scales with defined intervals and, in the case of ratio data, a true zero point. Therefore, nominal data distinctly lacks a measure of variability due to its categorical nature, making it the correct response in this scenario.