Question about calculating dates into different variables in MSAcc

[Guest]

I'm working on a research project where I'm comparing the number of visits
during the first 6 months and the second months of participation. So, I have
many subjects with multiple entries. What formula would you use to select
the first 6 months from the start date. Then, the second 6 months. Both to
be coded into 2 variables in a separate column or different table. Overall,
I'm trying to figure out how to calculate incidence rates. (I would hate to
do this manually.)

Also, how would you calculate total days of participation since start date?
Is there an easy way to determine if the collection dates fall within 30
days, 180, 270 days, etc, since start date.

Any helpful comments would be greatly appreciated. Still learning how to
code and use expressions. Thanks in advance.

 

[Allen Browne]

DateDiff() can give you a number of days, months, and so forth.
DateAdd() can set your date range.

This criteria will give you all entries within 6 months of the StartDate
field:
Between [StartDate] And DateAdd("m", 6, [StartDate])

Because you are want multiple columns, you could use a subquery for each
one. For Microsoft's introduction to subqueries, see:
How to Create and Use Subqueries
at:
http://support.microsoft.com/?id=209066