Which statement correctly describes nominal, ordinal, and interval data?

• A. Nominal data are categorical with an inherent order.
• B. Ordinal data have equal intervals between categories.
• C. Interval data are categorical with no natural zero.
• D. Nominal data are categories with no order, ordinal data are categorical with a meaningful order, and interval data are continuous with equal intervals.

Answer: (D)

The main idea here is the different levels of measurement: nominal, ordinal, and interval. Nominal data are categories with no inherent order—for example, blood types or species. Ordinal data are categories that do have a meaningful order, but the distances between the categories aren’t assumed to be equal—for example, pain scales or class rankings. Interval data are numeric with equal distances between values, and zero is not a true zero—for example, temperature in Celsius or Fahrenheit.

The statement that best fits these ideas says nominal data are categories with no order, ordinal data have a meaningful order, and interval data are numeric with equal intervals. That captures the essential distinctions. The other statements mix up these properties: nominal data aren’t ordered, ordinal data aren’t defined by equal intervals, and interval data aren’t categorical.