Convenience sample

Choosing individuals from the population who are easy to reach.

Voluntary response sample

Consists of people who have chosen to respond

Simple random sample (SRS)

Gathering a representative sample from a population where every group of size n has the same chance of being chosen. Each selection is independent.

Steps for choosing SRS

1. Label each individual with a distinct numerical value with the same number of digits

2. Randomize, either using technology or a list of random digits

3. Select the sample that corresponds to the selected integers

Systematic sample

The elements of the population are put into a list, and then every kth element in the list is chosen

Stratified sample

The population is divided into different subgroups, or strata, then are randomly selected proportionally

Cluster sample

Divide the population area into sections that are close to each other; randomly choose some of those clusters and include all members from those selected clusters.

Undercoverage

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

Voluntary response

Occurs when using a voluntary response sample. (not representative of pop)

Non-response

occurs when an individual chosen for the sample can't be contacted or refuses to cooperate (occurs after sample is taken)

Response bias

Occurs when there is a systematic pattern of inaccurate answers to a survey question; can be caused by the behavior of the respondent or the behavior of the interviewer.