In this session we will go through the meaning of sampling, sampling in qualitative research and types of sampling in qualitative research.

STUDY OBJECTIVES

What is sampling?

In statistics, quality assurance, & survey methodology,samplingis concerned with the selection of a subset of individuals from within a statistical population to estimate characteristics of the whole population.

In qualitative research, the termsamplingis taken tomean the process or action of selecting a set/s of specific people to be interviewed or observed for astudy.

Types of Sampling

There are two major types of sampling

1.Probability sampling

2.Non-Probability Sampling

Probability (Random) Sampling

This is the type of sampling in which all the individuals for a given study population have equal chance/s of being selected to participate in a given study in a random way. The aim of probability sampling is to find generalization of the results. This type is commonly used in quantitative studies and hence we will not spend time discussing it here.

Non-Probability

This type of sampling is also known as purposive sampling. It is the type of sampling where the individuals are selected with a purpose. That is the purpose of the study gives the direction to who should be interviewed. The selection of the study participants is based on their: knowledge of the subject under study, involvement in the subject/project under study, influence on the subject under study, role they play or how they are affected/ likely to be affected by the results/findings of the study and the available resources. It is from the basis of selecting study participants where the sample size in qualitative research becomes small.

This form of sampling is more common in the qualitative research arena. The common forms of purposive sampling are;

i.Purposive sampling

ii.Quota sampling

iii.Snowball sampling

 Purposive sampling

This is a type of sampling in which the study participants are simply selected from the pre-defined criteria (refer above). This is the most common used type of sampling in qualitative research. Purposive sample sizes are often determined on the basis of theoretical saturation (the point in data collection when new data no longer bring additional insights to the research questions). Purposive sampling is therefore most successful when data review and analysis are done in conjunction with data collection.

For instance in a study on Human resource for health retention in rural areas;

...for the qualitative data collection; the study population will include; The District Health Management Officials (District Medical Officer, District Health secretary, District Nursing Officer, District Pharmacist, District Dental surgeon and District Health Officer), the District Executive Director, the District hospital Medical Officer in charge, Chairman of the District Health Governing Board , the health centre medical in-charge, Chairman and Secretary of the Ward health committee, the dispensary Medical in-charge and Ward and Village Executives. It will also involve any available development partner/s that deals with health and any other key informant that will be identified and to be relevant in the process. This might also include informant from the Ministry of Health and Social Welfare (MoHSW) and from PMORALG. The qualitative data collection will also involve members of the ward and village Health committees. If these will be found to be non-functional the health centre and dispensary health committee will be used instead

Quota sampling

This is a form of purposive sampling in which decision of sample is made while designing the

study, how many people with which characteristics to include as participants. Characteristics might include age, place of residence, gender, class, profession, marital status, use of a particular contraceptive method, HIV status, etc. The criteria we choose allow us to focus on people we think would be most likely to experience, know about, or have insights into the research topic. Then we go into the community and - using recruitment strategies appropriate to the location, culture, and study population - find people who fit these criteria, until we meet the prescribed quotas.

Quota sampling is more specific with respect to sizes and proportions of subsamples, with subgroups chosen to reflect corresponding proportions in the population. If, for example, gender is a variable of interest in how people experience HIV infection, a quota sample would seek an equal balance of HIV-positive men and HIV-positive women in a given city, assuming a 1:1 gender ratio in the population. This is known as proportional quota sampling.

Studies employ purposive rather than quota sampling when the number of participants is more of a target than a steadfast requirement - that is, an approximate rather than a strict quota. This is referred to as non-proportional quota sampling.

Snowball sampling

This is a type of purposive sampling in which the already identified informant is used to identify another important informant that basically could not be identified by the researcher. Snowball sampling is also known as chain referral sampling. It is used often to find and recruit "hidden populations,” that is, groups not easily accessible to researchers through other sampling strategies.

When should you use purposive sampling?

Purposive sampling is used when:

1. Generalization of findings is not the aim of the study
2. Deep understanding is needed from expertise and not volume of information
3. Random sampling is not possible (Limited sample with variable characteristics)
4. Exploratory study
5. Limited budget, time and workforce

Summary

In this lecture we have gone through;

The meaning of sampling as a process of identifying and selecting study participants basing on our study purpose and how they fit to our study basing on our criteria we set. The criteria can be knowledge, age, gender, influence, involvement etc.

There are basically two major types of sampling which are; Probability (random) sampling which is commonly used in quantitative research and non-probability (systematic or purposive) sampling which is commonly used in qualitative studies. Purposive sampling has been further sub-divided to purposive, quota and snowball sampling.

Lastly we have seen when one should use non-probability sampling.

Self exercise

Using your own words distinguish between the three forms of purposive sampling.

Assignment

Develop a two page research concept note in which one of the purposive sampling strategy is going to be used.

Feed back

Dear Learner thank you very much for following, this mark the end of our lecture today.