Which aspect is crucial for establishing external validity in a study?

Establishing external validity in a study is fundamentally about ensuring that the findings can be generalized to a larger population beyond just the specific sample used in the research. The representativeness of the sample to the population is crucial because if the sample does not accurately reflect the characteristics of the broader population, then any conclusions drawn from that sample might not hold true for the entire population.

For example, if a study on a psychological phenomenon only includes college students and aims to generalize the findings to all adults, the sample is not representative of the entire adult population. Consequently, the results may not apply to those not included in the study, thereby compromising external validity.

While reliability of measurement instruments, the complexity of research design, and the consistency of results across different studies are important aspects of research, they do not directly pertain to the ability to generalize findings to a larger population. Reliability pertains to the consistency of the measures used in the study; complexity of design relates to the methodology; and result consistency across studies contribute to the understanding of a concept but do not guarantee that findings from a single study are applicable to broader settings or groups.