Qualitative research sampling methodologies
The benefits of a qualitative approach to many scientific fields of research are becoming increasingly recognized while doubts still arise about its philosophical basis and the methodological approach. Often, it is given the impression that qualitative research differs from any quantitative also in terms of data collection methods. The process of sampling is one of the principal areas of confusion; this is why quantitative and qualitative sampling methodological analysis can shed light into the basic differences between the two approaches. It further explains the reasons for which sampling techniques are not transferable between the two methods.
One of the most important and critical stages of any research is the choice of a study sample, given the fact that it is practically difficult, if not quite impossible, and costly either in time or financially to study whole populations. The aim of quantitative sampling approaches is to draw a representative sample so that through a cost-effective model the results are applicable back to the population and can be possibly generalized back to a wider field. The selection of the appro-priate method is strictly linked to the purpose and aims of the study. It isn’t uncommon for more “liberal” and less strict methods to be chosen, such as:
- Incidental sampling. It is considered the cheapest and easiest to imple-ment since the subjects are selected either because of the ease of their volunteering or because of their availability and ease of access
- Purposive sampling. It is also called judgmental sampling and its selec-tion is based on the knowledge of a population and the purpose of the study. The subjects are selected because they meet certain characteristics. This type of sampling seems useful whenever a targeted sample needs to be reached quickly and if proportionality isn’t the key aspect
- Quota sampling. It involves a preset number of cases in each sub-group of a specific population. It is useful when time and budget are limited but it suffers of unreliability in many cases since it can result to biased samples
- Snowball sampling or chain sampling. It consists of a non-probability method according to which existing subjects of a certain study recruit future participants that come either from their working place and/or are iden-tified as subjects that have knowledge relevant to the subject of the research
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