Sh.Sadeghi- Classification essay about types of sampling

Classification essay about types of sampling
Have you ever have to choose 50 persons among 100000? Is it occurs by chance? Can we do this selection in systematic way? In most of the researches a researcher has to choose small samples among a large population. But how it can be done? Based on which criteria we can choose the best samples which represent characteristics of population? In fact based on the nature of research we have different types of sampling. We have two main ways. The first one is probability. In this type the chance of each individuals are equal and it is based on chance. The second one, nonprobability, the purpose of researcher, effects on the selection.

In probability sampling we have 5 types that can be used for different research. The first one is simple. In this type each individual has an equal chance to be selected. For example we put 60 names in a container and then we choose 50 of them haphazardly.

The second one is the random sampling. In this one we list our samples in a table and then we choose the samples based on even or add numbers. In the third one, we select nth number of samples from n list. But we should notice before selecting we have to list our population. We call it as systematic sampling. The forth is stratified sampling. In this type at first we should divide our population into some subgroups which have the same characteristics. For example we can divide our population into men and women or graduated and no graduated. The last one is cluster sampling. According to its name we can understand gradually we reach to specific numbers of samples. This sampling is used when the geographic distribution is so wide or all number of samples isn’t available.

The second main type of sampling is nonprobability. In this group the chance aren’t equal for each samples and the bias of researcher effect on selection. It has 5 subgroups. The first on accidental or convince sampling. We choose our samples based on availability like interviewing in street. In purposeful sampling based on some features of participants we choose some participants who have the richest information to our research. Volunteer sampling isn’t representative of the total population.

It is clear that this sampling can’t show the main characteristics of population and it has strong bias. In another sampling we identify small number of individual who have the characteristic of researcher interest. Then we ask them to find samples who have the same characteristic like them self. We call this sampling as snowball. The last type of nonprobability sampling is quota sampling. In this type we use a portion or strata of population to do our research.

So, we can see that choosing samples for our research has important role on the results of our research. If we want to have generalizable results we should be careful about the type of our sampling and off course it is based on the nature of research. In summary we can classify sampling into two main groups: Probability and nonprobability. Each of these two groups has 5 types. In probability we have simple, Random, systematic, stratified and cluster. Accidental, purposeful, volunteer, snowball and quota are subgroups of nonprobability sampling