ABSTRACT
This chapter presents key methodological considerations and discusses research strategies and challenges in designing and applying a longitudinal study to examine intra-individual differences in Second language learning or use. In particular, it highlights the needs for researchers to understand the whole longitudinal research processes, obtain an adequate sample size necessary for quantitative analysis, and deals with quantitative analysis suitable for testing research hypotheses. During the planning stage of the study, it was important to think carefully about options for data analysis. To date, more publications in which researchers share their actual experience of and insight from doing longitudinal quantitative research are needed, so that new researchers or those interested in knowing more about longitudinal research can understand better what is involved in conducting a longitudinal quantitative study. Finally, researchers should not believe or attempt to convince others to believe that their study has made a significant contribution to the field merely because it is longitudinal.
