Non-Probability Sampling | Educational Statistics |

 

QUESTION

Explain non-probability sampling techniques used in educational research. 

Course: Educational Statistics

Course code 8614

Level: B.Ed Solved Assignment 

ANSWER

Non-Probability Sampling

This technique depends on subjective judgment. It is a process where probabilities cannot  be assigned to the individuals objectively. It means that in this technique samples are gathered in a way that does not give all individuals in the population equal chances of being selected. Choosing these methods could result in biased data or a limited ability to make general inferences based on the findings. But there are also many situations in which choosing this kind of sampling technique is the best choice for a particular research question or the stage of research.

There are four kinds of non-probability sampling techniques.

i)  Convenience Sampling

In this technique a researcher relies on available subjects, such as stopping people in the markets or on street corners as they pass by. This method is extremely risky and does not allow the researcher to have any control over the representativeness of the sample. It is useful when the researcher wants to know the opinion of the masses on a current issue; or the characteristics of people passing by on streets at a certain point of time; or if time and resources are limited in such a way that the research would not be possible otherwise. What may be the reason for selecting convenience samples, it is not possible to use the results from a convenience sampling to generalize to a wider population.

ii)  Purposive or Judgmental Sampling

In this technique, a sample is selected on the basis of the knowledge of the population and the purpose of the study. For example, when an educational psychologist wants to study the emotional and psychological effects of corporal punishment, he will create a sample that will include only those students who ever had received corporal punishment.  In this case, the researcher used a purposive sample because those being selected fit a specific purpose or description that was necessary to conduct the research.

Snowball Sample

This type of sampling is appropriate when the members of the population are difficult to locate, such as homeless industry workers, undocumented immigrants, etc. A snowball sample is one in which the researcher collects data on a few members of the target population he or she can locate, then asks to locate those individuals to provide the information needed to locate other members of that population whom they know. For example, if a researcher wants to interview undocumented immigrants from Afghanistan, he might interview a few undocumented individuals he knows or can locate, and would then rely on those subjects to help locate more undocumented individuals. This process continues until the researcher has all the interviews he needs and all contacts have been exhausted. This technique is useful when studying a sensitive topic that people might not openly talk about, or if talking about the issue under investigation could jeopardize their safety.

iv)  Quota Sample

A quota sample is one in which units are selected into a sample on the basis of pre-specified characteristics so that the total sample has the same distribution of characteristics assumed to exist in the population. For example, if a researcher wants a national quota sample, he might need to know what proportion of the population is male and what proportion is female, as well as what proportion of each gender fall into different age category and educational category. The researcher would then collect a sample with the same proportion as the national population.