Which of the following is NOT a primary assumption of parametric statistics?

• A. Data are normally distributed
• B. Variances of groups are equal
• C. Interval or ratio data
• D. Nominal data

Answer: (D)

Parametric tests rely on three core requirements: data measured at an interval or ratio level, groups with roughly equal variances (homogeneity of variance), and populations that are normally distributed. Nominal data, which are simple category labels with no inherent order or meaningful distance between categories, do not meet the measurement level needed for these tests. Because of that, nominal data are not a primary assumption of parametric statistics. When data are nominal or violate these assumptions, researchers typically turn to nonparametric methods or tests designed for categorical data. The other listed assumptions—normal distribution, equal variances, and interval/ratio measurement—are the standards that parametric procedures rely on.