Methodological considerations for the design and implementation of a fully longitudinal mixed methods study.

Growing interest is evident in longitudinal mixed methods research, particularly fully longitudinal mixed methods designs in which both quantitative and qualitative data are collected concurrently for the duration of the study. Fully longitudinal mixed methods designs are particularly relevant for research on dynamic phenomena because of their ability to illuminate both quantitative and qualitative dimensions of change in real time as the phenomenon of interest changes. However, these are complex research designs and their data-intense nature makes them potentially burdensome for study participants, challenging for research teams, and costly for funding agencies. Despite growing use, the methodological literature on fully longitudinal mixed methods research is sparse and little guidance is available for researchers considering this approach. We address this gap by describing our experience with the design and implementation of a fully longitudinal mixed methods study of a dynamic phenomenon, namely, family caregiving during cancer treatment. We describe important questions and key decisions confronted while developing the research proposal, proactive strategies for study implementation, and implementation realities encountered while the study was in progress. On the basis of insights gained through real-world experience, we offer three guiding principles for researchers undertaking such a study. First, align the study design with the nature of the dynamics in the phenomenon of interest. Second, plan from the start when and how the integration of the longitudinal quantitative and qualitative data will occur. Third, employ implementation strategies that take into account the practical aspects of repeated contacts with study participants for an extended period.