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What is the difference between a longitudinal study that follows subjects forward in time and a prospective study, which does the same?
For example why is the following a longitudinal rather than a prospective study?
"In a study, a group of people are exposed to an environmental toxin but are not treated. Instead, they are observed over time on a standard set of measures to ascertain the potential effects of the toxin."
Is it because it involves an intervention at the very beginning (the environmental toxin exposure) while a prospective study doesn't involve any intervention at all?
I'm confused here
Any replies will be much appreciated
First, remember horizontal and longitudinal. Horiz means from left to right or vice-versa. Longit means from top to bottom or reverse.
There are 2 studies – Experimental and Observational.
Longitudinal study is an OBSERVATIONAL only and it is done by Cohorting.
Cohort has 2 methods:
1. PROSPECTIVE – when you start counting the cases from present time (today) to onwards (till tomorrow or uncertain FUTURE times)
2. RETROSPECTIVE- when you start searching ( &collecting) the cases from today to PREVIOUS days ; i.e. PASSED time cases
In other words: all Prospective studies are longitudinal studies but longitudinal studies are NOT ONLY Prospective studies! Prosp study itself is a Longi but Longi can be also a Retrosp.
For your specific question:
Longi does multiple observations for EACH INDIVIDUAL over a certain period of time.
Prosp does multiple observations for a GROUP OF PEOPLE over a certain period of time.
Actually, there is no much difference between these two terminologies; and I think one can use both. But the term longitudinal is more specific than other.
This is what I know about it.
PS.!I want to know from other colleagues whether I am right as well.
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