A pizza restaurant wants to know who eats more pizza – people from Daly City or people from Colma. To find out, the restaurant hired people to stand in front of the Target store in both cities and ask people how much pizza they eat per week. They talked to 1000 people from each city. 1. (2 pts.) Is this an observational study or an experiment?
Observational Study (there is no manipulation of any variables to look for a cause-effect relationship)
5. (2 pts.) Name a potential confounding variable in this study. Explain why it is confounding.
There are many. One good one that some of you said was: income level (people who shop at Target are probably in the middle class, excluding poor/rich people).
6. (2 pts.) Describe a potential flaw in the sampling plan.
People shopping at Target come from all over, not just Daly City or Colma. There was no mention of if the sample was chosen at random – it MUST be random in order to draw conclusions about the overall population.
7. (2 pts.) In an experimental study: what is the purpose of double-blinding?
The purpose of double-blinding is to avoid bias by making sure that the subjects (people who receive a treatment) do not know what treatment they are getting (placebo or otherwise) as well as those administering the treatments (who might be emotionally inclined to give someone a particular treatment) and by making sure that the researchers who analyze the resulting data do not know which group they are analyzing (and perhaps bias the data in a particular way).
For questions #8-13, use the following scenario:
Some friends of mine want to know if eating pizza makes you gain weight. To find out, they gather 30 people and randomly divide them into two groups. The people in one group eat pizza once a day for two weeks. The people in the other group do not eat pizza for the two weeks. All the people are weighed before and after the two weeks. 8. (2 pts.) Is this an observational study or an experiment?
This is an experiment (they are randomly dividing them into groups and telling the subjects what to do – eat pizza or not)
9. (2 pts.) What population is being studied?
10. (2 pts.) What is the explanatory variable in the study?
11. (2 pts.) What is the response variable in the study?
Weight gain (or not)
12. (2 pts.) Name a potential confounding variable in this study.
There are many answers. One that I think was particularly good was exercise – if you exercise a lot, you could lose weight even if you eat pizza.
13. (2 pts.) Describe a potential flaw in the study design.
There are many answers. One that was particularly good was that the experimenters are not controlling the food consumption outside of the pizza eaten. They should try to control for that variation more.
14. (2 pts.) In an observational study: what is the purpose of a random sample?
To create a sample that resembles the population so that you can generalize results found in a sample to the overall population.
15. (2 pts.) Describe one way to establish a cause-and-effect relationship between two variables.