Does the presence of invalid measures in research affect internal validity or external validity?

The presence of invalid measures in research primarily affects internal validity. Internal validity refers to the extent to which a study can demonstrate a causal relationship between variables, ensuring that the observed effects are truly due to the manipulation of the independent variable rather than extraneous factors. When invalid measures are used, it undermines the reliability of the data collected, leading to potential inaccuracies in the results. This means that the conclusions drawn from the study may be flawed, as the measures may not accurately assess the constructs they are intended to evaluate.

On the other hand, external validity pertains to the generalizability of the study's findings beyond the specific circumstances under which the research was conducts. While invalid measures could have some indirect effects on how findings might be generalized, the primary concern lies with how accurately the study measures what it claims to measure, which is directly tied to internal validity.

Therefore, the correct answer emphasizes that invalid measures directly compromise the study's ability to produce valid and trustworthy conclusions, which is essential for establishing internal validity.