Correct Answer: C — External validity (generalizability)

Key validity concepts in research:

Concept	Definition	Used In
Internal Validity	The study truly measures the effect of the IV on DV (free from confounders)	Quantitative
External Validity	Findings can be generalized to other populations, settings, or times	Quantitative
Transferability	Qualitative equivalent of generalizability — findings may apply to similar contexts	Qualitative
Credibility	Qualitative equivalent of internal validity — truth value of findings	Qualitative

Generalizability requires a representative sample from the target population. Random sampling enhances external validity, while convenience sampling limits it.