In statistics, different methods or techniques are used to obtain sample data from a given population. These methods or techniques are known as sampling techniques. Broadly, these can be classified into 4. They are:
Random Sampling :
As the name suggests, data is extracted randomly. There isn't any specific order to acquire the data. In this, every member of the population has an equal chance of being selected for your sample.
Some examples: lottery, movie reviews from crowds etc
Stratified Sampling :
In stratified sampling, the data is extracted based on the group/layers/clusters. For example: In the exit poll, only those people are interviewed whose age is above 18. Similarly, men and women are interviewed separately to get an unbiased result based on gender and population distribution.
Systematic Sampling :
In systematic sampling, every nth term is selected from the population. This nth term is dependent upon the user who is extracting the data.
Example: A salesman approaching every 5th customer that enters the mall.
Convenience Sampling :
Only those data are selected which are easy to attain. For example, a survey regarding new technology will only be conducted on those people, who are interested in technology. These people will provide themselves for the survey.
In this short article, I have tried to explain the most commonly used sampling techniques. Hope, it helps.