Purposive sampling
In qualitative research, exploring the range and nature of views, experiences and behaviours (including how survey questions are understood and answers arrived at) is important, more than the extent to which they occur in the population of interest, which is the realm of quantitative inquiry.
In an ideal world qualitative investigation would be based on grounded theory: the process of data collection and conceptualisation continues until 'saturated' - that is, new data do not add to the developing theory. However, because of resource constraints it is more practical to sample respondents for qualitative data capture purposively. Respondents are chosen because they have particular features or characteristics which will enable detailed exploration of the research objectives. It is important to note that it is not possible to draw statistical inferences from this kind of sampling method since, with a purposive non-random sample, the number of people interviewed is less important than the criteria used to select them.
Data Collection Methodology (DCM) is able to use a register of former survey respondents who have agreed to be contacted about future research by the Office for National Statistics. This provides a large number of potential respondents from the general population, across the whole country, from which we can select people with the characteristics of interest to approach to take part.
If the register is not suitable because of the characteristics of interest, other sampling methods can be used, such as 'snowballing' (people with the characteristics of interest identifying people they know with those characteristics) or contact through appropriate channels such as employers, organisations and associations. DCM does not use specialist recruitment agencies but conducts its own recruitment.
