Karen O'Reilly

My book Qualitative Research Methods for Everyone: An Essential Toolkit was published by Policy Press in March. In the book, I confront the thorny issue of qualitative sampling, and I introduce the idea of initial, ongoing and final samples and of sample fitness rather than sample size 

Interpretive Sampling

First, I introduce the concept of Interpretive Sampling. An interpretive sample will be iterative-inductive, constantly iterating between being inductive (open-minded, bottom-up, learning from the field) and deductive (testing out existing and new theories and concepts to see if they help clarify understandings), with an inductive approach retaining the upper hand.

In qualitative research we usually aim to represent types of people or behaviours, or a range or diversity of experiences or perceptions, as these relate to the problem we are addressing and in the context of certain conditions. However, there is a good chance that we do not know at the outset what typologies will be meaningful, how diverse the responses will be or what conditions are relevant. We must start somewhere, with an initial sample, but this may not remain adequate.

Initial Sample 

The initial sample is designed purposefully to include groups, individuals, or other characteristics that can logically or thematically be taken to be representative of the population. This sample is representative of the wider population conceptually, not numerically – or in terms of quality not quantity. 

Not only is designing an initial sample a sensible and logical way to proceed but those giving funds, permission or access for your work will need an idea how you intend to start.

Ongoing samples

Interpretive sampling continues as the research proceeds, through ongoing assessment of the relevance of data for your eventual findings and, where possible, making adjustments to who and what are included. 

Ongoing sampling involves returning to (more or the same) people, to examine emergent ideas, new topics, developing insights, and reviewing what and who is included as analysis proceeds. In the design of a project or proposal, I explain to readers why ongoing sampling will be crucial and how that will be practically achieved, perhaps through convenience or snowball sampling. 

Final samples 

The final sample is the people, groups, contexts, and other variables and topics you finally included; they reflect required relevant diversity for specific outputs. It is important that the sample you end up with gives you confidence to be able to say what you want to say. 

I will talk about sample fitness in my next blog. 

Thanks for reading!