Population and Samples

Populations

A group of people, places or things that have a least one common characteristic.

(Vincent and Weir, 2012)

Sample

Portion or fraction of a population

(Vincent and Weir, 2012)

Inferences

We make inferences from a sample back to the population as long as our sample is representative of the population

Representative sample

“a sample or subgroup of a population that is similar to the population on the characteristics of interest”

(Baumgartner and Hensley, 2006, p. 117)

Biased sample

“Not representative of a population”

(Hall and Getchell, 2014, p.177)

= poor external validity

Random Sample

Procedure for the selection of participants for a study that provides an equal chance of selection for all members of the population

Stratified Random Sample

The population is divided (stratified) on the basis of some characteristic before random selection of the sample”

(Thomas et al., 2015, p. 106)

Systematic sample

Procedure for the selection of participants in a study in which every nth individual on a list is selected.”

(Hall and Getchell, 2014, p.176)

Cluster sampling

Instead of sampling individuals from the population, “clusters” are randomly sampled

Convenience sampling

selecting the research participants on the basis of being accessible and convenient to the researcher”

(Baumgartner and Hensley, 2006, p. 124)

Inclusion criteria

Characteristics individuals must possess in order to qualify for participation in a study.

Exclusion criteria

Characteristics individuals cannot possess in order to qualify for participation in a study.