How does instrumentation threaten a study's internal validity?

• A. By introducing measurement error
• B. By altering the subject's behavior
• C. By affecting the training of researchers
• D. By changing the research question mid-study

Answer: (A)

Instrumentation threatens a study's internal validity primarily by introducing measurement error. This can occur when the tools or instruments used to measure a variable are inconsistent, unreliable, or flawed in a way that affects the data collected. For instance, if a survey instrument is modified during the course of the study or if there is a discrepancy in how researchers measure the same behavior at different times, the resulting data may not accurately reflect changes in the participants or the effects of the intervention being studied. As a result, the conclusions drawn from the study may be compromised because the observed changes could be attributed to the inaccuracies in measurement rather than to the effects of the treatment or intervention itself.

This factor is crucial in maintaining the integrity of a study’s findings, as internal validity hinges on the ability to confidently assert that changes in the dependent variable are indeed caused by manipulations of the independent variable, rather than by extraneous factors such as measurement inconsistencies.