Final answer:
The difference between non-concurrent and concurrent cohort studies lies in the approaches to data collection over time. Concurrent cohort studies are prospective, actively following participants, while non-concurrent studies are retrospective, analyzing pre-existing data.
Step-by-step explanation:
The question 'Non-concurrent vs concurrent cohort study refers to differences in:' relates to b) Approaches to longitudinal data collection in studies. A cohort study is an observational study where a group is followed over time. In concurrent (or prospective) cohort studies, researchers actively follow participants to record results, hence maintaining a high level of accuracy. In contrast, in non-concurrent (or retrospective) cohort studies, researchers look back at existing data or records to analyze outcomes.
Longitudinal research is crucial for observing changes over time in a particular group, while cross-sectional research offers a snapshot of different groups at one point in time, providing a more immediate but less dynamic understanding. Case-control studies are also retrospective, like non-concurrent cohort studies, but primarily focus on comparing people with a particular condition to those without.
Each type of observational study, including cohort, cross-sectional, and case-control studies, carries its own advantages and challenges which researchers must consider when designing a study.