How many interviews or focus groups are enough?

When it comes to qualitative evaluation data, is more always better and what determines value for money? This article proposes two steps for evaluators and those responsible for procuring evaluations to answer the question ‘how many interviews or focus groups are enough?’ Step 1 is to consider the nature of the evaluation question to determine the sampling goal, importance of thematic saturation, and an appropriate sampling strategy. The article provides guidance on how many interviews and focus groups are needed to achieve different levels of thematic saturation based on empirical tests in the published literature. Step 2 is to check the skills of the evaluator, including whether they integrate behavioural science into their discussion guide and analysis to mitigate bias. This will determine – regardless of the number of interviews and focus groups – whether they will be able to generate useful insights for decision-making from the data. The article concludes that it is not sufficient to assess an evaluation plan’s value for money by sample size alone and consideration also must be given to the characteristics of the evaluation design and the skills of the evaluators undertaking the project.