Abstract
Many clinical studies require the longitudinal collection of data over time. As data collection may not be uniformly collected on each patient (e.g., blood tests may be performed regularly in some patients and sporadically in others), it is important to understand the frequency and patterns of data collection events over time so that statistical analyses can be planned. We demonstrate the use of a graphical technique, the FU-PLOT (short for Follow-Up PLOT), that can assist research investigators and statisticians in visualizing the frequency and patterns of follow-up data collection. Examples are from a longitudinal study of children born to mothers infected with the human immunodeficiency virus (HIV). The method can be adapted to a variety of situations, and is easily programmed in most graphics, spreadsheet, and statistical packages.