Sampling and Surveys

Population

a statistical study is the entire group of individuals we want information about

Census

collects data from every individual in the population

Sample

a subset of individuals in the population from which we collect data

Sample Survey

a study that collects data from a sample to learn about the population from which the sample was selected

Convenience Sampling

selects individuals from the populations who are easy to reach

Bias

if a statistical study is very likely to underestimate or overestimate the value you want to know

Voluntary Response Sampling

allows people to choose to be in the sample by responding to a general invitation

Random sampling

involves using a chance process to determine which members of a population are included in the sample

Simple Random Sample (SRS)

of size n is chosen in such a way that every group of n individuals in the population has an equal chance to be selected as a sample

Sampling without replacement

an individual from a population can be selected only once

Sampling with replacement

an individual from a population can be selected more than once

Strata

are groups of individuals in a population who share characteristics thought to be associated with the variables being measure in a study

Stratified random sampling

selects a sample by choosing an SRS from each stratum and combining the SRSs into one overall sample

Cluster

a group of individuals in the population that are located near each other

Cluster sampling

selects a sample by randomly choosing clusters are including each member of the selected clusters in the sample

Systematic random sampling

selects a sample from an ordered arrangement of the population by randomly selecting one of the first k individuals and choosing every kth individual thereafter

Undercoverage

occurs when some members of the population are less likely to be chosen or cannot be chosen in a sample

Nonresponse

occurs when an individual chosen for the sample can’t be contacted or refuses to participate

Response Bias

occurs when there is a systematic pattern of inaccurate answers to survey question