Promises and pitfalls of qualitative longitudinal research

This commentary focuses on promises and pitfalls of qualitative longitudinal research (QLR). Longitudinal data on practices, perspectives, individual relevancies and experiences can be particularly advantageous for life course, social policy and health research. However, the complexity of QLR carries certain downsides, dilemmas and trade-offs. The commentary discusses implications of different qualitative methods for the investigation of stability and change, the tensions between flexibility and comparability, and challenges related to sampling and the explanatory power of QLR.It is argued that the choices of methods for data collection and data analysis have stark implications for what can be determined as change and stability across time. In addition, several ways of ensuring comparability across time are described. Finally, sampling strategies are outlined that aim to achieve and maintain heterogeneity of cases.As standards of good practice, the author advocates more thorough documentation of the methods of data collection, sampling and data analysis employed in QLR studies, along with a better description of instruments and how they are applied.