Non-probability sampling is that type is which the selection of sample is not based on probability but the personal judgment of the researcher play a significant role in the selection of the sample. Following are the important types of Non-probability sampling.
- Purposive Sampling.
- Quota Sampling.
- Accidental or Incidental Sampling.
- Convenience Sampling.
- Self-Selected Sampling.
- Sequential Sampling.
- Extensive Sampling.
- Replicated Sampling.
In this case sample is not selected by the researcher but the member of the universe offers themselves for selection. Suppose an inquiry is to be made by the people about an issue, an advertisement is published in newspaper. The people come volunteer and particulate in the study and acts as subject of the study. They attend the meeting on their own will and present themselves for selection of sample.
It is the type of non-probability sampling in which data is collected from the specified number of individuals. The group of these individuals is called quota. That quota is specified on the basis of age, sex, education etc. called quota-control factors. For example, quote of male and female, old and young, upper and lower, rural and urban, educated & uneducated etc.
Accidental or Incidental Sampling
Accidental or incidental is that type of sampling in which a researcher pick up data or information’s from those who fall into hand or present at the time of research. It continues the process till the completion of the sample size. It is accidental because it is selected accidentally from all type of people comes to face like, teacher, students, house wife, tailors, workers, etc.
Selecting convenient population units is called convenience sampling. It refers to that part of population being selected on convenience. For example sampling of automobiles registrations and telephone directories but this method is not representative to the whole universe because every person does not possess automobile or telephone.
Sequential sampling in which the selection of sampling size is not fixed in an advance but a researcher select elements until a decision reached and he stop sampling. This method was adopted during 2nd World War for rapid decisions.
A purposive sampling is that on which is selected by the choice and free will of the researcher. A researcher selects sample according to the needs and requirements of the study. Such a sample is said to be biased and discriminatory because of self-selection.
Extensive sampling is less or more resemble to census method in which the entire universe is studied and no unit is left out expect the irrelevant items. Suppose if we study the opinion of Pakistan educated person about the future family system, we dropped out the non-Pakistani and uneducated from out sampling and will interview the rest of individuals.
Replicated sampling is a sort of non-probability sampling where two independent samples are taken using the same sample procedure by different investigators. It means that the sample is repeated or relocated by one research from that of the other.