Biology Forums - Study Force

Define the terms "stratified sampling", "systematic sampling", "cluster sampling", and "convenience sampling". Give examples for each.

Stratified sampling subdivides the population into at least two different subpopulations and then draws a sample from each stratum. Systematic sampling selects a beginning point and then selects every kth element in the population. In cluster sampling, the population is divided into sections, then sections are randomly selected, and then all members of the randomly selected sections are surveyed. Convenience sampling uses readily available results.

Stratified sampling- For example- geographical regions can be stratified into similar regions by means of some known variable such as habitat type, elevation or soil type. Another example might be to determine the proportions of defective products being assembled in a factory. In this case, sampling may be stratified by production lines, factory, etc.
For example, you can select individuals from the voter's list in each stratum to say rural and urban.  You can have villages or urban wards selected from the strata which have both stratification and cluster sampling.
Example: Suppose a supermarket wants to study buying habits of their customers, then using systematic sampling they can choose every 10th or 15th customer entering the supermarket and conduct the study on this sample.
Convenience sampling is a non-probability sampling technique where subjects are selected because of their convenient accessibility and proximity to the researcher.