A researcher surveys 50 students from her own course about spending habits. Why would this study have low external validity?

• A. Cross-Sectional Design
• B. Convenience Sampling
• C. Random Sampling
• D. Large Sample Size

Answer: (B)

External validity is about whether findings apply beyond the exact people studied. Surveying 50 students from her own course uses a convenience sample—participants chosen because they were easy to reach. That creates a biased group, likely sharing traits such as same institution, same course, and similar backgrounds, which may not reflect students in other courses, other colleges, or the broader population. Because the sample isn’t representative, the observed spending habits may not generalize, leading to low external validity. The issue here is how the sample was chosen; random sampling would improve representativeness, while the size or a cross-sectional design don’t by themselves determine generalizability.