Sampling

Who? How many? Selection? Sorted?

Information:

Gender

Age

Geographical area

SES

Source

Basis for participation

Other

Population:

All the units we would like to study

The people who are the focus of the research

Sample:

A group of people who represent the population

Keep record of:

Number contacted

Number participated

Number screened out and why

Number dropped out and why

Probability sampling:

Simple random

Systematic sampling

Stratified random

Cluster

Nonprobability sampling:

Convenience

Purposive

Snowball

Quota

Sampling error:

Random

Systematic

Probability theory:

To estimate how closely sample statistics are clustered around the true population value.

Large samples

Numerous samples

Randomness (sample with replacement)

Randomness is necessary in order to use powerful statistics!