Sampling and Observational Studies
This lecture series discusses the studies conducted using surveys. You can use surveys to obtain information about a group of people, but it can be impossible to survey each person if the group is very large. The limited number of people surveyed is called a sample. The way a sample is selected can affect the outcome of a study and its validity. Watch the videos and complete the interactive exercises.
Practice
Generalizability of results - Answers
1. Only the top 
longest streaks worldwide in June
The 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 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 
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 
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.