The validity of nutrition research is crucially dependent on the selectiion of a proper sampling technique. In this post , we will cover the various sampling methods used by researchers, along with their applications.
Types Of Sampling Methods
Sampling methods can majorly be categorized as:
- Probability sampling methods are sampling techniques where a
researcher sets a selection criteria to aid in selecting members of a population
randomly. - Non-probability sampling methods involve the selection of participants in a non-random manner.
Types of Probability Sampling Methods
Simple random sampling– It is a sampling method whereby each member of a population has an equal probability of being selceted. The selection is solely by chance. For example, in a class, the researcher wants a few participants to join hin for a trip. He may probably hand out sheets of paper in a container-some of them blank and others with a tick. Those who get the sheets of paper with a tick are quaified to go for the trip with him. In such an instance, all the members in the classroom have an equal chance of being selected.
Stratified sampling-It involves classifying the population into sub-groups(strata) that share similar qualities, and do not overlap with each other. Then the sample participants are selected randomly from each strata.
Systematic sampling -The sample participants are selected at fixed intervals -every nth respondent is selected. For example, a researcher can decide that every 5th person in the population under study is chosen. Therefore, the 5th person, will be the first one chosen , followed by the 10th , then the 15th and so on.
Cluster sampling -A selected population is grouped into clusters which may be selected based on demographic variables such as sex, marital status, education level, occupation, income etc. then prospects are randomly selected from the clusters.
Probability sampling methods are important when the researcher needs an accurate sample, is dealing with a broad population that is diverse or if he wants to reduce bias so that each member has an equal chance of being selected.
Types of Non-probability Sampling Mehods
Quota sampling -It is a rapid sampling method that involves the selection of study participants based on pre-determined standards. The researcher sets a target for the various groups and then selected persons who fit the specific criteria are sampled until they fill a quota. For example, a researcher targets to interview 600 undergradutae students studying nutrition, and sets the criteria as follows:
4th year students-200 participants
3rd years -150 participants
2nd year -150 participants
1st year -100 participants
Once the researcher fills a quota, let’s say he already interviews the 150 respondents in 3rd year , he will not allow any additional applicants from 3rd year.
Purposive sampling-Study participants are chosen at the researcher’s discretion based on qualities that align with the purpose of the study. For example, if a study aims to understand the challenges experienced by nutrition professionals in hospital settings, the researcher will only focus on nutritionists working in hospitals, not those in industries or in community projects etc.
Convenience sampling -It is based on the selection of subjects’ easy accessibility perhaps due to close proximity. It is less representative as participants are chosen merely based on their accessibility. Such studies are mainly conducted due to either cost or time constraints in data collection.
Snow balling sampling-Utilized for discretionary or highly-sensitive subjects. For instance, where study participants may be required to disclose their health staus i.e. if tehy have an STI. The researchers may have to send their assistants to contact the respondents to gather information.
Non-random sampling methods are used by the researcher when he wants to develop a hypothesis , is experiencing time or budget limitations or when he seeks to explore a topic.