Systematic differences between volunteer research participants and the general population can limit the generalizability of study findings, creating issues for ________ validity.

Why does relying heavily on volunteer participants often create a problem for a study's external validity?

A researcher recruits volunteers for a study on a new memory-improvement technique by advertising specifically to members of a high-IQ society. After finding significant results, the researcher can safely conclude that the technique will be equally effective for the general population because the participants were eager volunteers.

A researcher finds that a cognitive training program—which was highly successful with a group of self-selected volunteers—fails to show any benefit when applied to the general population. Arrange the following steps in the logical order a researcher would take to analyze how the participants' characteristics limited the study's generalizability.

Match each research recruitment scenario with the evaluative judgment that best identifies how volunteer bias threatens the study's external validity.

To test a cognitive-enhancement technique for the general public, you must design a recruitment protocol that minimizes the risk of a sample with higher-than-average education or IQ. Which of the following strategies would you develop to best ensure the findings are applicable to the average person?

True or False: Because volunteer participants are highly motivated to participate in research, volunteer bias typically enhances a study's external validity by making the findings more generalizable to the broader population.

Arrange the following statements in the correct logical sequence to demonstrate how volunteer bias ultimately threatens a study's external validity.

Match each research scenario with the specific volunteer characteristic that most likely threatens its external validity.

When analyzing why an intensive study-skills program was highly effective for self-selected student participants but showed no effect when mandated for the entire student body, a researcher identifies that the volunteers had uniquely high baseline motivation. By isolating how this systematic difference prevents the initial findings from generalizing to the broader population, the researcher demonstrates that volunteer bias has directly compromised the study's ________ validity.