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Re: st: Difference in dates


From   Nick Cox <njcoxstata@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Difference in dates
Date   Sun, 15 Jul 2012 21:44:58 +0100

Evidently if the dates are really the same, the result of calculating
the difference should be 0.

So this question is immediately bounced back to you: what are your
grounds for your contradictory statement? What makes you say these two
things?

Note that either or both being assigned a daily date format is purely
a cosmetic matter, as that just affects what is displayed, and is only
indirectly related to what the value _is_, meaning _is stored as_.
Otherwise put, non-integers will display as if they were (integer)
dates if assigned a daily date format.

. di %td mdy(7,15,2012) + 0.5
15jul2012

. di %td mdy(7,15,2012) + 0.6
15jul2012

. di %td mdy(7,15,2012) + 0.9
15jul2012

. di %td mdy(7,15,2012) + 1
16jul2012

You should look at the date variables using a non-date display format.
Presumably at least one has been calculated incorrectly at some
previous point.

Nick

On Sun, Jul 15, 2012 at 8:48 PM, Lisa Davis <lisadavismd@gmail.com> wrote:

> I'm comparing two date variables (coded daily) in Stata by subtracting one from a second, which gives a difference in days. When the dates are the same, the result is 0.5 rather than 0. Does anyone have an explanation?
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