Sampling
the entire group of individuals we want information about
population
Observational study or experiment: Ninety residents of a retirement community were selected at random. Each member of the sample was asked a number of questions, including questions about exercise and blood pressure.
observational study
Some members of the population are less likely to be chosen or cannot be chosen for the sample
undercoverage
provides a baseline to compare the treatment against
control group
selecting individuals who are easy to reach
Convenience sampling
Give an example of a non-statistical question
How much money does Mr. Tagawa have in his wallet right now?
When people can’t be contacted or refuse to answer
nonresponse
changes are seen from a fake treatment, usually a psychological effect
placebo effect
only surveying people who chose to be in the sample
voluntary sampling
What type of sampling: From the population of all MHS students, randomly select 10 homerooms and survey everyone in those homerooms
cluster sampling
Example: A non-anonymous survey about cheating on tests might lead students to lie
response bias
the patient doesn't know if they received a real treatment
single-blind study
What type of sampling is this: From the population of all MHS students, randomly select 10 freshman, 10 sophomores, 10 juniors, and 10 seniors.
stratified sampling
What type of sampling: From the population of all MHS students, pick every 3rd student from an alphabetized list of all the students.
systematic random sampling
outside factors that might be the real reason for a certain observation
confounding variables
How can you decrease variability in your samples?
increase the sample size
What is the goal of doing an experiment?
to understand the cause and effect relationship between two variables
What is the purpose of using random assignment?
To create groups that are roughly equivalent