The most important question to ask when interrogating the external validity of a sample is option b) how was the sample collected?
External validity refers to the generalizability of the research findings to other populations or settings beyond the specific sample used in the study. To assess external validity, it is crucial to understand how the sample was selected and whether it is representative of the larger population to which the researchers want to generalize their findings.
The method of sample collection is critical because if the sample is not representative of the target population, the results may not be generalizable. For example, if the sample was self-selected or recruited through convenience sampling, it may not accurately reflect the characteristics of the broader population, limiting the external validity of the findings.
On the other hand, options a) how many people are in the sample, c) how were the participants measured, and d) how many people are in the population, while important considerations, are not as directly relevant to assessing the external validity of the sample as the sampling method itself.
The size of the sample (option a) and the population (option d) can affect statistical power and precision but do not necessarily speak to the representativeness of the sample. Similarly, the measurement methods (option c) are more relevant to the internal validity and reliability of the study but do not directly address external validity and generalizability.
Therefore, the most important question to ask when interrogating the external validity of a sample is how the sample was collected, as this directly impacts whether the findings can be generalized to other populations or settings.