Final answer:
The most pertinent question to ask when assessing the external validity of a study with an unrepresentative sample is whether the biased sample characteristics are relevant to what is being measured. This question directly pertains to the possibility of generalizing the results to a broader population.
Step-by-step explanation:
When assessing the external validity of a study that uses an unrepresentative sample, the most pertinent question to ask is "Are the characteristics that make the sample biased relevant to what is being measured?" This question addresses the heart of the issue with external validity, which is whether the results obtained from the sample can be generalized to the broader population. Factors such as the study's claim type and sample size do not directly address the representativeness of the sample, whereas the relevance of the sample's biased characteristics to the study's measured outcomes does.
For instance, if a study aims to measure the effectiveness of a software tool in a group undergoing an exercise program versus a group not using the tool or exercising, the inclusion of the exercise variable may introduce bias. Therefore, the study's conclusions about the software tool's effectiveness would likely be invalid if generalized to a population that is not engaged in such a program. Similarly, sampling error and nonsampling error can affect the validity of the results, as with a low response rate or biased sampling methods like convenience sampling.