Longitudinal quantitative research designs

In this paper I aim to present some of the advantages and problems associated with longitudinal quantitative research designs. The main feature of longitudinal designs is that the effect of time on the subjects of the research can be studied better than in cross-sectional designs where several groups (called cohorts), or one cohort divided up on the basis of a feature such as age, may be required. If you compare two groups on the basis of age you cannot assume that any differences you observe are due to age - this is known as the cohort effect. However, longitudinal designs bring some problems in terms of keeping subjects in the study and the longer the time between points at which stages of the study are carried out, the greater the difficulty in retaining subjects. In addition to these general features of longitudinal quantitative research designs, some specific designs and methods of statistical analysis will be considered.