What is instrumentation threat to internal validity?

• A. It occurs when participants drop out of the study.
• B. It occurs when the independent variable is not properly manipulated.
• C. Instrumentation threat occurs when measurement tools or procedures change across the study, affecting scores.
• D. It occurs when sample size is too large.

Answer: (C)

Instrumentation threat to internal validity happens when the tools or procedures used to measure outcomes change during the study, so the scores reflect these changes rather than true effects of the manipulation. This can occur if a test is revised, scoring rubrics are updated, observers become more lenient or strict, or measuring equipment drifts in calibration. Such shifts introduce systematic differences that confound the treatment effect. By contrast, attrition (participants dropping out) relates to who stays in the study, and issues with how the independent variable is implemented concern treatment administration, while a very large sample size mainly affects power, not measurement consistency.