Which example illustrates a nominal variable?

A nominal variable is a type of categorical data that represents different categories without any intrinsic order or ranking among them. Blood type fits this definition perfectly because it classifies individuals into distinct groups (A, B, AB, O) without implying any hierarchy or sequence.

In contrast, income levels and education levels represent ordinal data, meaning they can be ranked or ordered based on some criterion—higher or lower incomes and varying levels of education can be compared. Economic statuses, while they may also seem like categories, often involve a ranking as they usually describe a spectrum of social class. Therefore, blood type distinctly stands out as a nominal variable, as it simply categorizes without any need for an order.