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
Identify the population and sample - Questions
1. The state Department of Transportation wants to know about out-of-state vehicles that pass over a toll bridge with several lanes. A camera installed over one lane of the bridge photographs the license plate of every tenth vehicle that passes through that lane.
Identify the population and sample in this setting.
Choose 1 answer:
(A) The population is all of the vehicles that pass over the toll bridge; the sample is vehicles from the lane with the camera.
(B) The population is all of the vehicles that pass through the lane with the camera; the sample is the group of every tenth vehicle that passes through the lane.
(C) The population is all of the out-of-state vehicles; the sample is the vehicles that pass over the toll bridge.
2. A group of librarians is interested in the numbers of books and other media that patrons check out from their library. They examine the checkout records of 
randomly selected adult patrons.
Identify the population and sample in this setting.
Choose 1 answer:
(A) The population is all adult patrons of the library; the sample is the 
patrons selected.
(B) The population is all patrons of the library; the sample is the adult patrons of the library.
(C) The population is all patrons who check out at least 
book from the library; the sample is the patrons selected.
3. A pediatrician randomly selected parents of his patients. Then he surveyed the parents about their opinions of different kinds of diapers.
Identify the population and sample in this setting.
Choose 1 answer:
(A) The population is the parents of the pediatrician's patients who wear diapers; the sample is the parents of all of the pediatrician's patients.
(B) The population is the pediatrician's patients; the sample is the patients selected.
(C) The population is the parents of the pediatrician's patients; the sample is the parents of patients selected.
4. A city council member wanted to know how her constituents felt about a planned rezoning. She randomly selected 
names from the city phone directory and conducted a phone survey.
Identify the population and sample in this setting.
Choose 1 answer:
(A) The population is everyone listed in the city phone directory; the sample is the people selected.
(B) The population is residents of the city; the sample is the registered voters in the city.
(C) The population is registered voters in the city; the sample is everyone listed in the city phone directory.