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Re: st: snapsan command


From   sara bonfanti <sara.bonfanti@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: snapsan command
Date   Mon, 21 May 2012 09:41:12 +0200

I will try to formulate my problem in a clearer way...

I have no problem in running the snapsan  and the stcox command and I
have understood their purpose.

Still,after running the snapsan command I get an output I don't
exepct, namely the missing values.

My question is why such missing are generated?  The manual says
nothing about it (it just shows a picture of the dataset converted to
a time-span form which contains missing values in the first row) and
the other Stata users I've talked to couldn't explain it either.

Furthermore, If I run the stcox command and Stata ignores the missing
value created after running the snapsan command, can I consider the
output of my cox regression reliable?

Thanks

Sara

2012/5/19 Nick Cox <njcoxstata@gmail.com>:
> The command is -snapspan-, not -snapsan-. I think you didn't get an
> answer to this previously because it's hard to work out what you want.
> The tenor of your posting is "I don't understand" and that evokes
> sympathy, but it is hard to know what explanation could make it
> clearer than that in the manual.
>
> The answer to 1) is that it depends what you mean "when I work on my
> variables". Depending on that, the possibilities include nothing (the
> Stata command will ignore missing values), using -if- to exclude
> observations with missing values, and using -drop- to drop them.
>
> The answer to 2) is No. -generate()- is genuinely optional.
>
> For "STATA" read "Stata". For "cox" read "Cox".
>
> Nick
>
> On Sat, May 19, 2012 at 10:05 AM, sara bonfanti <sara.bonfanti@gmail.com> wrote:
>
>> I'm stuck with my work beacuse of these problems.
>>
>> I'm using STATA 12.1. In order to run a cox regression (stcox) I have
>> reshaped my dataset form wide to long and, then, I have run the
>> command
>> "snapsan".
>>
>> I wonder:
>>
>> 1) why, after running the command "snapsan", I get for each individual
>> a first row (corresponding to the first year of my longitudinal
>> database,
>> i.e. 1997) of missing values except for the event variable. Reading
>> the stata manual it seems a correct output but I don愒 know how to
>> deal with these missing values later on, when I work on my variables.
>>
>>
>> 2) if it愀 necessary to specify the option "generate(newt0var)". I
>> have found it on manuals, but still I don愒 understand how it works,
>> and why I should use it.
>>
>
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