RESEARCH METHODOLOGY

Detailed explanation-1: -In a longitudinal study, there are observations over time but no true experimental design or manipulation. So the study may be termed ‘correlational’, which is the critical word you see in the Wikipedia article. So basically, repeated measures design = experimental; longitudinal analyses = observational.

Detailed explanation-2: -A repeated-measures design is one in which multiple, or repeated, measurements are made on each experimental unit. The experimental unit could be a person or an animal, and repeated measurements might be taken serially in time, such as in weekly systolic blood pressures or monthly weights.

Detailed explanation-3: -Repetitio est mater studiorum [Repetition is the mother of learning]. Medical research often involves study designs in which the same outcome variable is repeatedly observed or measured over time in the same study subjects (patients). Such repeatedly measured data are referred to as longitudinal data.