Nonprobability sampling has no element of chance and likelihood. It means that the selection of elements from the population of interest is not random, but according to our discretion and purpose, in this type of sampling. Though nonprobability sampling is more economical and easier than probability sampling but its use is still very limited in the field of research and most research prefer to use probability sampling in their research. The main reason of its less popularity is that we can’t estimate the confidence interval when sampling in this way. In other words, we can’t say how confident we would be about the result of our study or how much our sample would be a true representative of the population of interest if we adopt this method of sampling. But it doesn’t mean that we should not use it at all. Sometimes it is not convenient or practically possible for us to conduct probability sampling for our research, therefore we use nonprobability sampling. Following are some of the well known types of nonprobability sampling.
1. Convenience Sampling:
In convenience sampling we select only the most conveniently available elements of the population of interest e.g. friends, relatives, colleagues, shoppers on the mall, school-mates etc. Typical kinds of convenience sampling include:
i. Persons On The Street Sample
ii. Shopping Mall Intercept Sample
iii. Intact Group Sample
iv. Fortuitous Sample
2. Purposive Sampling:
In this kind of sampling we select only those elements from the population which best suit the purpose of our study.
3. Judgmental Sampling:
A judgment sample is obtained when we select elements from the population based upon our own judgment or according to the recommendation of someone else that is well familiar with the relevant characteristics of population.
4. Referral or Snowball Sampling:
In this kind of sampling we don’t have a prior knowledge of the elements of population; therefore we take help from the first element we select for the sample. Put simply if we want to conduct a study about the relationship between a certain drug and its impact on our health. It may be possible that we don’t know about the users of that drug. But if we find the first user he can tell us about the 2nd user and so on.
