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# Re: st: time-series data identified by three variables

 From YANNAN SHEN To "statalist@hsphsun2.harvard.edu" Subject Re: st: time-series data identified by three variables Date Fri, 30 Nov 2012 04:58:27 -0500

```Hi Nick,
There is one more thing I need your help with. Within each group where there is a patient return to treat the same disease, I want to calculate the duration between the repeat visit with his first visit .
I wrote the following code:
> bysort patient_id illness_id date: gen duration = date[_n]-date[1]
but it returns all zeros.
What is wrong?

Sent from my iPhone

On Nov 28, 2012, at 4:21 AM, Nick Cox <njcoxstata@gmail.com> wrote:

> You want commands like
>
> bysort patient_id illness_id date of visit : egen meansev = mean(severity)
> by patient_id illness_id : gen repeat = _n - 1
>
> as you want to number 0 upwards.
>
>
> Nick
>
> On Wed, Nov 28, 2012 at 6:28 AM, yannan shen <yannan2010@gmail.com> wrote:
>
>> I am working some panel data of hospital visits and I want to learn
>> the severity of various disease.
>> The variables I have in the dataset are: patient_id, illness_id,
>> date_of_visit, severity
>> each observation contains: patient_id, illness_id, date_of_visit, severity.
>>
>> For each patient (identified by patient_id), I want to know how many
>> of times he has visited for the same illness （illness_id ).
>> I use the duple command to to label the observation of patients who
>> have visited hospital more than once.
>>
>>> duplicates tag  patient_id illness_id , generate(duple)
>>
>> However, duple does not give information for any time series
>> information. If a patient has 5 visiting records, I want to be able to
>> know which is the 0th repeat, 1st repeat, 2nd repeat, 3rd repeat, and
>> 4th repeat...I have a vague feeling that I can order those variables
>> via date_of_visit but I am still not sure how exactly that can be
>> done.
>>
>> Furthermore, I want to create two new variables: one variable equals
>> to the average severity of each disease (disease_id) being treated on
>> the same date_of_visit. The other variable equals the highest severity
>> of a certain disease being treated on that day. (Ideally, I want to
>> create additional variables for each observation)
>>
>> I have used “bysort” in the past but since now the type is a
>> combination of illness_id and date_of_visit， I am a little confused.
>
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