Drop-out in the context of psychological research is a common and significant phenomenon. However, it is difficult to estimate its exact relevance and negative implications for research, particularly in terms of validity. The aim of this paper is thus to highlight the importance of considering participant drop-out in clinical research, in order to develop a theoretical frame for sampling technique, capable of considering those aspects that are currently barely considered. Specifically, the paper will focus on paradigms and methods in relation to sampling. Subsequently, possible explanatory and predictive variables of the phenomenon will be discussed. Finally, a longitudinal study on the transition to parenthood in primiparous couples will be presented as an example, due to its high drop-out rates after the first phase of participation.
Keywords: Sampling, drop-out, explanatory variables