Chapter 1 Flashcards
what are Categorical variables
places each case into one of several groups or categories ex: gender, race, music genre
what are quantitative variables
takes numerical values for which arithmetic operations such as adding and
averaging make sense
Examples: income, weight, heart rate
What does the distribution of a variable tell us
The values that a variable takes and how often it takes each value
Define population
A group of individuals which we want info about
Define sample
a part of the population from which we actually collect information
List some problems with taking a census
- people can be hard to locate
- populations rarely stand still
- a census may be more complex than sampling
Non-response bias
if only a small fraction of the randomly sampled people choose to respond to the survey.
The population may no longer be represented appropriately
Under-coverage
some groups in the population are left out of the process of choosing the same
Examples: A household survey will miss homeless people and people in jail or dorms
Voluntary response bias
The sample consists of people who volunteer to respond because they have strong opinions on the issue
Response Bias
Lying, or forgetting the truth
What is an observational study?
Where researchers collect data in a way that doesn’t interfere with how the data arises
ie: they observe instead of ask
What is a retrospective study?
Collect data after events have taken place
What is a simple random sample?
Randomly selecting cases from the population, where there is no implied connection between the points that are selected.
Each member has an equal chance to be selected.
What is a stratified Sample?
Strata are made up of similar observations
- We take a simple random sample from each stratum
What is a cluster sample?
take a simple random sample of clusters, then sample all observations in that cluster
- preferred for economical reasons
