What can decrease the external validity of a study?

The choice indicating that the sample not being representative of the population can decrease the external validity of a study is accurate. External validity refers to the extent to which the findings of a study can be generalized to, or have relevance for, settings, people, times, and measures beyond the specific conditions of the study.

When a sample is not representative, it means that the specific group of participants selected for the study does not accurately reflect the broader population that researchers intend to draw conclusions about. This mismatch can lead to results that cannot be reliably applied to the larger population, undermining the study's external validity. For example, if a study focuses exclusively on a homogenous group, its findings may not hold true for a more diverse or different population.

In contrast, effective random sampling increases the likelihood that the sample will accurately mirror the population, hence supporting external validity. Clear operational definitions help ensure that a study's variables are measured consistently, which contributes to internal validity but doesn't directly relate to how well findings translate beyond the study context. A large sample size can enhance statistical power but does not automatically ensure that the sample is representative, which is crucial for maintaining external validity.