What characteristic of parallel assessments refers to measuring the same trait on all forms of the test?

• A. Internal consistency
• B. Fairness
• C. Vertical scalability
• D. Unidimensionality

Answer: (D)

Measuring the same trait across every form relies on a single underlying attribute being targeted by each version. That idea is unidimensionality—the test, across its forms, is designed to tap one main trait or ability. When forms share this focus, scores can be compared as they reflect the same construct even though different items are used.

Internal consistency, by contrast, describes how well the items on one form hang together to measure the trait within that form, not across different forms. Fairness concerns bias and equal opportunity rather than whether the forms assess the same trait. Vertical scalability relates to tracking growth or difficulty levels over time, not the sameness of the trait across forms.

So, the characteristic described is unidimensionality.