Which statement correctly differentiates cross-classified data from hierarchical data structures?

• A. A unit can be nested under two units simultaneously in cross-classified data.
• B. A unit can be nested within only one higher-level unit in hierarchical data.
• C. They are identical in structure.
• D. Cross-classified data involves only time-based nesting.

Answer: (B)

In data structures for analysis, hierarchical (nested) data have observations that sit inside a single higher-level unit, creating a clear, one-path nesting down the hierarchy. Cross-classified data, on the other hand, allow observations to be linked to multiple higher-level groupings that are not nested within each other, so there isn’t just one parent level.

Saying that a unit is nested within only one higher-level unit in hierarchical data directly states the defining contrast to cross-classified structures. If each observation has a single, exclusive higher-level container, that’s the hallmark of nesting, distinguishing it from the cross-classified situation where multiple groupings can apply to the same unit.

The alternative would describe a feature of cross-classified data—being associated with more than one higher-level group—rather than defining what makes hierarchical data distinct. The essential distinction is the single-nesting property of hierarchical data.