Here is a timely example of random sampling in action.
Watch this 2-minute video about the CDC's project in Atlanta (produced by NPR). It explains how nurses are visiting about 500 people in the Atlanta metropolitan area to see how widespread the Coronoavirus is. In the first minute of the video, the narrator reports,
The CDC is sending out employees to conduct antibody tests on a random sample of Atlanta residents. The tests are meant to show how many people have been infected with the Coronavirus.
The CDC wants to get blood samples from 450 households.
(Note: And here's another story of a similar effort, this time in Corvallis, Oregon, USA. It's about prevalence of live cases, rather than antibodies, but a random sample is still a key player.)
Questions:
a) Why would it be important to conduct antibody tests on a random sample of people from the Atlanta area?
b) The plan is to collect samples from 450 households. Imagine that a friend hears this figure and expresses skepticism--"how can 450 be enough to generalize to the population of Atlanta?" Explain to your friend why a random sample--even if it has "only" 450 households--can generalize to the population.
c) What are some ways the CDC might conduct this random sample? Review the possibilities in Chapter 7 and explain:
i) how might they obtain a simple random sample of Atlanta residents?
ii) how might they obtain a cluster sample (what could they use as clusters?)
iii) how might they conduct a stratified random sample? (Imagine that they want to use neighborhoods/zipcodes as the strata.)
d) After conducting the antibody study on a random sample of Atlanta residents, the CDC will have an estimate of the rate of infection in the sample. To whom will they be able to generalize this rate of infection--that is, to which population of interest?
e) What might happen if some of the randomly sampled people in Atlanta refuse to have their blood drawn for this CDC study? Will that affect the sample's generalizability? Why or why not?
f) Which big validity is this example concerning?
Many thanks to Dr. Jess Harnett (of the notawfulandboring blog), who posted this example, and thanks to Kathy Becker-Blease for sharing the Oregon example.
