Categories of Sampling Categories of Sampling TechniquesTechniques

Statistical ( Probability ) Sampling:Statistical ( Probability ) Sampling:– Simple Random SamplingSimple Random Sampling– Stratified Random SamplingStratified Random Sampling– Cluster Random SamplingCluster Random Sampling– Systematic SamplingSystematic Sampling

Non-Statistical (Non-Probability) Non-Statistical (Non-Probability) SamplingSampling– Judgment SamplingJudgment Sampling– Convenience SamplingConvenience Sampling

Simple Random SamplingSimple Random Sampling

Simple Random Sampling is a Simple Random Sampling is a method of selecting method of selecting nn units out of units out of a population of a population of NN such that every such that every one of the one of the NNCCnn distinct samples has distinct samples has an equal chance of being drawn.an equal chance of being drawn.

P(any sample of n from a P(any sample of n from a population of N) is equal to the population of N) is equal to the reciprocal of reciprocal of NNCCnn..

Stratified Random Stratified Random SamplesSamples

In stratified sampling, the population of N units In stratified sampling, the population of N units is first divided into sub-populations of Nis first divided into sub-populations of N11, N, N22, … , … NNLL units, respectively. These sub-populations units, respectively. These sub-populations (strata) are non-overlapping, and together (strata) are non-overlapping, and together comprise the whole of the population, so that comprise the whole of the population, so that NN11+N+N22+…+N+…+NLL= N When the strata have been = N When the strata have been determined, a sample is drawn from each determined, a sample is drawn from each stratum. The sample sizes within the strata are stratum. The sample sizes within the strata are denoted by ndenoted by n11, n, n22, … n, … nLL

Cluster SamplingCluster Sampling

Cluster sampling is a method by which the Cluster sampling is a method by which the population is divided into groups, or population is divided into groups, or clusters, and a sample of clusters is taken clusters, and a sample of clusters is taken to represent the population. Clusters to represent the population. Clusters should be representative of the entire should be representative of the entire population.population.

The objective is to form groups of clusters The objective is to form groups of clusters that are small images of the target that are small images of the target population.population.

Systematic SamplingSystematic Sampling

For systematic sampling, elements For systematic sampling, elements of the population are categorized in of the population are categorized in some way (such as alphabetically some way (such as alphabetically or numerically) and a random or numerically) and a random starting point is selected. Then starting point is selected. Then every Nevery Nthth item of the categorized item of the categorized population is included until the population is included until the sample size n is satisfied.sample size n is satisfied.