Re: st: repeated time values within panel

[Nick Cox <njcoxstata@gmail.com>]

That is not really addressing the point.

-xtset- needs to be set specifying a time variable ahead only of
commands that require a time variable; which commands do you envisage
using with that requirement?

The fact is that your dataset is one in which ties on year exist and
are natural, so no -xt- method that requires unique (id, time)
observations will make sense any way.

Stata itself recognises this distinction by _not_ requiring a time
variable to be set; you may specify a panel identifier and that alone
in -xtset-.

Nick
njcoxstata@gmail.com


On 6 September 2013 00:41, Momplaisir, Florence
<Florence.Momplaisir@tuhs.temple.edu> wrote:
> Thanks for your response Nick. My understanding is that adding the time variable tells stata that the order of observations within the panel matter i.e. that there is a time order (here baby year of birth) within the panel. This is important because moms with multiple babies can have controlled HIV disease on their first pregnancy but not on their second or third pregnancies.
> ________________________________________
> From: owner-statalist@hsphsun2.harvard.edu [owner-statalist@hsphsun2.harvard.edu] on behalf of Nick Cox [njcoxstata@gmail.com]
> Sent: Thursday, September 05, 2013 10:50 AM
> To: statalist@hsphsun2.harvard.edu
> Subject: Re: st: repeated time values within panel
>
> Backing up here: What is your reason for setting a time variable here?
> Clearly your mothers define panels, but  different mothers have
> children at quite different times. -xtset Stateno- may be as much as
> you really need. Nothing stops you using the year as a covariate for
> most other purposes. Which commands do you want to run that require a
> time variable to be set?
>
> Nick
> njcoxstata@gmail.com
>
>
> On 5 September 2013 15:37, Momplaisir, Florence
> <Florence.Momplaisir@tuhs.temple.edu> wrote:
>> Hello,
>>
>> I'm working with a longitudinal dataset using surveillance data on HIV+ women during pregnancy and at delivery. In the dataset, women have multiple pregnancies and some have multiplets (twins, triplets etc). I'm using the xtset command to run a regression with the woman (Stateno variable) and the year as the time variable. Here is the error I found:
>>
>> xtset Stateno birthyr
>> repeated time values within panel
>> r(451);
>>
>> And this is because I have twins that have repeated time values, i.e. repeated time measures. How do I get ride of that duplicate without deleting from the dataset?
>
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