Representative sample
A subset of a population that reflects the population’s relevant characteristics closely enough to support conclusions about it.
Simple random sampling: A sampling method in which every population member has an equal chance of selection. Equal selection chances reduce systematic exclusion, though chance variation can still produce an unbalanced sample.
Statistical population: The complete set of units about which a statistical study seeks to draw conclusions. A sample is representative only in relation to a defined target population.
Convenience sampling: A nonprobability sampling method that selects units because they are readily available. Ease of recruitment can produce a sample unlike the population it is meant to reflect.
Survey sampling: The selection of units from a population to collect information through a survey. Survey design uses sampling procedures to make population estimates defensible.
Stratified sampling: A method that divides a population into strata and samples from each stratum. Sampling within relevant groups helps preserve their representation in the final subset.
Sampling unit: The unit selected during sampling, such as a person, household, school, or region. The chosen unit shapes who or what the sample can include.
Self-selection bias: Bias that arises when people’s decision to participate is related to study-relevant characteristics. Voluntary participation can make the final sample systematically unrepresentative.
Opinion poll: A survey designed to measure public attitudes or preferences at a particular time. Poll accuracy depends on who is included, who responds, and how answers are measured.
Cluster sampling: A method that randomly selects groups, or clusters, from a population for study. It can lower collection costs, but selected clusters may not reflect the whole population.
Population parameter: A numerical characteristic of an entire population, such as its mean or proportion. A representative sample aims to support estimates of relevant population parameters.