What is a longitudinal design? an experiment that is conducted so that neither the experimenter nor the participants are aware to which group the participants belong a procedure in which one or more variables are manipulated while all the other variables are held constant systematic observation that involves obtaining measures of the variables of interest in multiple waves over time the extent to which an experimental design is representative of the real-world issues it is supposed to address

A longitudinal design is a systematic observation that involves obtaining measures of the variables of interest in multiple waves over time.

Explanation:

A longitudinal design is a type of research that seeks to observe the behavior of one or more variables through time, it is helpfull in the understanding of change and variation. In order to do so, systematic observation is involved on different occasions over the course of the research.

In a longitudinal design the sample must remain the same during the time of the study, in order to identify changes and variations.