Which property measures the degree to which items within an assessment are related and measure the same construct?

The property that measures the degree to which items within an assessment are related and measure the same construct is internal consistency. This concept assesses whether different parts of a test or items within a scale consistently reflect the same underlying trait or construct. For example, if a questionnaire is designed to measure anxiety, internal consistency evaluates whether the individual questions yield similar responses, indicating that they are all effectively capturing the concept of anxiety.

Internal consistency is typically quantified using statistical methods, such as Cronbach's alpha, which provides a coefficient that ranges from 0 to 1, with higher values indicating better consistency among the items. A high internal consistency suggests that the items are well-designed and are working together cohesively to measure the intended construct, contributing to the reliability of the assessment.