What is internal validity?

• A. Internal validity is the extent to which findings generalize beyond the sample.
• B. Internal validity is the extent to which a study demonstrates a causal relationship between variables, free from confounding factors.
• C. Internal validity refers to the reliability of measurement instruments.
• D. Internal validity relates to how quickly data were collected.

Answer: (B)

Internal validity is about whether a study can confidently establish a causal link between the manipulated variable and the observed outcome by ruling out other possible explanations. It ensures that confounding factors aren’t driving the results, which is why designs use random assignment, control groups, consistent procedures, and sometimes blind procedures to minimize bias. When internal validity is high, we can say that the changes in the dependent variable are due to the independent variable, not something else. This is different from external validity, which concerns generalizing findings beyond the study, and from reliability, which concerns whether measurements are consistent. For example, if two groups differ in caffeine intake or testing times, those differences could produce the observed effect rather than the intended manipulation, undermining internal validity. The other options refer to generalizability, measurement consistency, or data-collection speed, which do not address establishing causation within the study.