Probability sampling

Selection biases are decreased when using probability sampling

There are three types of probability sampling. Probability sampling means that participants have an equal chance of being selected for participation in the study. Probability sampling or random selection, when paired with random assignment, allows for researchers to make causal inferences regarding treatment effects using experimental designs. Researchers choose a probability sampling method based on answering their specific research questions and the need for representing subgroups or clusters of the population. Click on one of the buttons below to continue.

Three types of probability sampling

Every member of a population has an equal chance of being selected for participation in the study.  
Simple Random Sampling
Independent strata within a given population are randomly sampled. Each stratum must be overtly defined and homogeneous in some relative way. Simple random sampling is then conducted on the stratum (singular) or strata (plural) of interest. 
Stratified Random Sampling
Naturally occurring or defined subgroups of a given population are randomly sampled. The subgroups need to be defined and are often grouped according to socioeconomic, demographic, clinical, or theoretical characteristics.
Clustered Random Sampling
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Sample Size
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There are three probability sampling methods: Simple random sampling, stratified random sampling, and clustered random sampling.