Final answer:
The main difference between RCT and longitudinal cohort designs is how data is collected and tracked over time.
Step-by-step explanation:
One main difference between a randomized controlled trial (RCT) design and a longitudinal cohort design is the way the data is collected over time. In an RCT, participants are randomly assigned to different groups and the study intervention is applied to one group while the other serves as the control. The data collected is usually based on specific outcomes or measurements at predetermined time points. On the other hand, in a longitudinal cohort design, a group of similar subjects (the cohort) is selected at the start of the study and followed over time. Data is collected periodically, allowing researchers to track changes and observe development or progression of disease states or conditions of interest in the cohort over a longer period of time.