Population
The entire group of individuals that we want information about
Sample
A part of the population that we actually examine in order to gather information
Sampling
Involves studying a part in order to gain information about the whole
Census
Attempts to contact every individual in the entire population
Convenience
Chooses the individuals easiest to reach
Biased
Systematic errors in the way the sample represents the population
Simple random sample
Consists of all individuals from the population chosen in such a way that every set of individuals has an equal chance to selected as a sample
A table of random digits
A table consisting of long strings of digits, each equally likely to be chosen and are independent of each other
Probablility Sample
A sample chosen by chance
Stratified random sample
Divides the population into groups of similiar individuals called strata and chooses a simple random sample or SRS in each stratum then combines these SRS's to form a full sample
Undercoverage
When some groups in the population are left out of the preocess of choosing the sample
Nonresponse
When the individual chosen for the sample cant be contacted or do not cooperate
Sampling frame
The list of individuals from which a sample is actually selected
Observational studies
Observes individuals and measures variables of interest but does not attempt to influence the responses
Experiment
Deliberately imposes some treatment on individuals in order to observe their response
Probablility sampling design
Uses impersonal chance to select samples
Multistage samples
Successively selects smaller groups within the population in stages, resulting in a sample consisting of clusters of individuals
Response bias
Bias due to the behavior of the interviewer or the respondent