Reconciling the Quantitative and Qualitative Traditions—The Bayesian Approach

Qualitative research is often ‘hypothesis generating’ and so determines the agenda for quantitative research, as well as often helping to provide tools (for example instruments for measuring outcomes). The results of qualitative research can also influence decisions directly. This article explains how the results of qualitative research can be taken into account when making policy decisions. The authors argue that this should be done explicitly: the decision-maker should ‘convert’ the qualitative data into a quantitative ‘prior’ belief about the true value of the key parameter(s) on which the decision turns and then use Bayes' law to combine the ‘prior’ with (any) comparative quantitative results to produce a ‘posterior’ quantitative belief about the key parameter. This produces transparency—it allows proper assessment of the impact of qualitative data on the analysis and assumptions behind this impact.