Sampling and Observational Studies

1. Only the top $$$200$ longest streaks worldwide in June

The $200$ longest streaks weren't randomly selected from a larger population. They are not representative of all players in the world or Canada-they are the top $200$ longest streaks of all players.

2. All students at the university who participate in the intramural football league

Since the sample was randomly selected from students who participate in the university's intramural football league, the results can safely be generalized to this population.

3. Anyone who has taken a yoga class at the gym in the past year, but not before that

Since the sample was randomly selected from anyone who had taken a yoga class at the gym in the past year, the results can safely be generalized to this population.

4. Only those viewers who called in

The viewers who called in weren't randomly selected, and they are likely not representative of any larger group. Viewers who took the time to call in likely have stronger opinions than those who didn't call in, or different opinions than those who don't watch this show.

5. All first-year students, but only those who live in these $12$ residence halls

Since the sample was randomly selected from first-year students who live in those residence halls, the results can safely be generalized to this population.

6. All homes in that city, but not the entire state

Since the sample was randomly selected from all homes in that city, the results can safely be generalized to this population.

7. The dermatologists at that session only

The $15$ dermatologists at this session weren't randomly selected from a larger population. They may not be representative of all doctors or even all dermatologists on the question of experience.