Re: st: Changing values future time points conditional on value from prior time point

[Jeph Herrin <info@flyingbuttress.net>]

this should do

 bys id (time) : replace c_heartcond=1 if c_heartcond[_n-1]==1


cheers,
Jeph


On 2/24/2014 4:50 PM, Kaufmann, Christopher N. wrote:
> I am working with data from a longitudinal cohort study with five time points.  The dataset is formatted in a "long" format. I would like to change values of a variable for future time points conditional on the value of the variable in a prior time point. Below is an example of the structure of my dataset in its current form:
>
> ID     Time    c_heartcond
> 1      1       0
> 1      2       1
> 1      3       0
> 1      4       1
> 1      5       0
> 2      1       0
> 2      2       0
> 2      3       1
> 2      4       1
> 2      5       0
>
> ID = participant identification number
> Time = time points of the study
> c_heartcond = participant reported that they have a heart condition since the last time they were interviewed (1 = yes, 0 = no)
>
> As you can see, a person can report a heart condition at one time point, but report that they didn’t have a heart condition the next time point. I would like to change the c_heartcond variable so that all future time points after the first that the subject reported the heart condition have a value of 1.  For example:
>
> ID     Time    c_heartcond
> 1      1       0
> 1      2       1
> 1      3       1
> 1      4       1
> 1      5       1
> 2      1       0
> 2      2       0
> 2      3       1
> 2      4       1
> 2      5       1
>
> I have written code to do this.  See below:
>
> *Fixing comorbidity:
> foreach var of varlist c_heartcond c_stroke c_hypertension c_pain c_arthritis c_cancer c_diabetes c_incontin c_memorydis {
>    if c_order_expand == 1 & `var' == 1 {
>      foreach x1 in 2 3 4 5 {
>        replace `var' = 1 if c_order_expand == `x1'
>        }
>      }
>    if c_order_expand == 2 & `var' == 1 {
>      foreach x2 in 3 4 5 {
>        replace `var' = 1 if c_order_expand == `x2'
>        }
>      }
>    if c_order_expand == 3 & `var' == 1 {
>      foreach x3 in 4 5 {
>        replace `var' = 1 if c_order_expand == `x3'
>        }
>      }
>    if c_order_expand == 4 & `var' == 1 {
>      foreach x4 in 5 {
>        replace `var' = 1 if c_order_expand == `x4'
>        }
>      }
>    else {
>      replace `var' = `var' if c_order_expand == 5
>      }
>    }
>
>
> But when browsing through the data after running this code, I notice that there are instances where this data is not formatted correctly.  For example, the data might look like this after running my code:
>
> ID     Time    c_heartcond
> 3      1       1
> 3      2       0
> 3      3       0
> 3      4       0
> 3      5       0
>
> Thank you for any help that you can provide.
> *
> *   For searches and help try:
> *   http://www.stata.com/help.cgi?search
> *   http://www.stata.com/support/faqs/resources/statalist-faq/
> *   http://www.ats.ucla.edu/stat/stata/
*
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