Final answer:
A nationwide sample of people ages 18 to 25 is most likely to generalize to Matt's population of interest.
Step-by-step explanation:
The sample that is most likely to generalize to Matt's population of interest, young adults ages 18 to 25, is a nationwide sample of people ages 18 to 25. This is because a nationwide sample would include a diverse range of young adults from different geographical locations, backgrounds, and demographics, which would make it more representative of the overall population. The other samples, such as attendees of a gaming convention or people in Matt's hometown, may not provide as accurate of a representation of the wider population.