The use of mixed methodology in evaluating complex interventions: Identifying patient factors that moderate the effects of a decision aid

Background. Mixed method research, the combined use of qualitative and quantitative methods, is increasingly popular in health services research, especially as a way to examine 'complex interventions'. This paper seeks to provide a case example of the use of mixed methods in the analysis of a complex intervention (a computerized interactive decision aid) to test whether their use affords insights into potential moderators of the intervention (i.e. patient factors that were associated with the impact of the intervention). Methods. We conducted a pragmatic randomized controlled trial (n = 149) of a decision aid in women attending their primary care practitioners with menorrhagia. Alongside the trial, a qualitative study was conducted with interviews with a sample of women who had received the intervention (n = 18). Hypotheses generated by the qualitative study were used to inform subsequent quantitative subgroup analyses. Results. The results from both studies showed that the decision aid was broadly beneficial. The qualitative study found that women with less formal education reported greater levels of benefit from the intervention. However, quantitative analyses of formal education as a moderator of treatment effect found that the intervention provided the greatest benefit in women with greater formal education. The findings of the qualitative and quantitative studies thus demonstrated a significant inter-method discrepancy. Possible reasons for this discrepancy are discussed. Conclusions. Mixed methods can illuminate different aspects of an intervention or provide greater insight into particular issues. Health service researchers need to be aware that the qualitative and quantitative results may be discrepant, and methods need to be developed to deal with such discrepancies. However, exploring seemingly discrepant results can lead to greater insight and the development of new hypotheses and avenues of research. © The Author 2007. Published by Oxford University Press. All rights reserved.