Sampling can be explained as a specific principle used to select members of population to be included in the study.
“A sample is some portion of a population. Because many populations of interest are too large to work with directly, techniques of statistical sampling have been devised to obtain samples taken from larger populations.” (Proctor, 2003, p.100).
According to Saunders et al (2007) sampling is one of the most crucial components of studies that involve the collection of primary data from the population. The choice of a sampling technique identifies a principle by which members of population are selected to be included in the sampling group. Moreover, it has been stated that “any statistical method that requires a certain size of sample to be collected to satisfy requisite levels of confidence” (Sharp et al, 2002).
Sampling involves selecting some members of population to be involved in the study for primary data collection upon s specific sampling principle. Researchers warn that “the sampling technique(s) you select largely depends on whether or not you wish to infer that your findings apply to the wider population. However, you may not wish to generalise, but aim to provide a ‘snapshot’ of one particular case, e.g. asking business customers what they think of one particular delivery process to one particular supplier, rather than to all suppliers” (Wilson, 2010, p.189).
Sampling methods are broadly divided into two categories: probability and non-probability.
In probability sampling methods, there is a known, non-zero probability of being chosen for each population member. Popular probability sampling methods are stratified, random and systematic sampling methods.
In non-probability sampling methods, on the other hand, population members are selected on the basis of a specific non-random technique. Such non-random techniques, i.e. non-probability sampling methods include snowball, convenience, quota and judgement sampling methods.
Brown (2006) summarises the advantages of sampling in the following points:
a) Makes the research of any type and size manageable;
b) Significantly saves the costs of the research;
c) Results in more accurate research findings;
d) Provides an opportunity to process the information in a more efficient way;
e) Accelerates the speed of primary data collection.
Hair et al (2007, p.171) describe the following set of procedures to obtain representative sample from population:
- Defining the target population.
- Choosing the sampling frame.
- Selecting the sampling method.
Generally, sampling procedures for this research has involved the following four stages:
Stage one: defining the population. It has been noted that “defining population is not always straightforward. It largely depends on your research questions and the context with which you wish to study. When defining your population, you need to establish the types of case that make up your population, e.g. individuals, firms, households, etc” (Wilson, 2010, p.190).
Stage two: definition of the sampling frame. “Sampling frame means the list of all units comprising the population from which a sample is to be drawn” (Avasarikar and Chordiya, 2007, p.5-11). In other words sampling frame is a list of people among the population that have a chance of participating in the survey.
Stage three: determining the sample size.
The following observations need to be taken into account when determining sample size:
- The magnitude of sampling error can be diminished by increasing the sample size.
- There are greater sample size requirements in survey-based studies than in experimental studies.
- Large initial sample size has to be provisioned for mailed questionnaires, because the percentage of responses can be as low a 20 to 30 per cent.
- The most important factors in determining the sample size include subject availability and cost factors
Stage four: selection of the sampling method.
Brown RB, 2006, Doing Your Dissertation in Business and Management: The Reality of Research and Writing, Sage Publications
Hair, JF, Jr., Money, AH, Samouel, P, Page, M, 2007, Research Methods for Business, John Wiley and Sons, Ltd
Proctor, T, 2003, Essentials of Marketing Research, 3rd edition, Prentice Hall
Sharp, JA, Peters, J & Howard, K, 2002, The Management of a Student Research Project, third edition, GOWER
Saunders, M, Lewis, P, Thornhill, A, 2007, Research Methods for Business Students, 4th edition, Prentice Hall
Wilson, J. (2010) “Essentials of Business Research: A Guide to Doing Your Research Project” SAGE Publications