Lab6 Solution

Part I

1. Start Stata, open your do-file editor, write the header, and load transplants.dta.

2. ctr_id indicates the ID of the transplant center where the patient received the transplant. Count the number of recipients at each center, and store in a new variable volume.

   bysort ctr_id: gen volume=_N
   

3. List ctr_id and volume to see how many patients each center has. Maybe let’s try this:

   list ctr_id volume

4. Whelp. This is not what we wanted. Generate a variable ctr_tag that “tags” one observation per center.

   egen ctr_tag=tag(ctr_id)
   

5. Now list ctr_id and volume, but just for one record per center.

   list ctr_id volume if ctr_tag==1
   

6. Calculate the mean age of the patients at each center, and store in a new variable mean_age.

   bys ctr_id: egen mean_age=mean(age)
   

7. For each primary diagnosis subgroup (use variable dx), run a regression with age as the predictor and peak PRA (peak_pra) as the outcome.

   forvalue i=1/9 {
           regress peak_pra age if dx==`i'
   }
   

8. Now let’s make the output cleaner. Count the number of cases within each diagnosis group. If there are more than 500 cases, run the regression and display the output. If not, display “There are fewer than 500 cases.”

   forvalue i=1/9 {
       qui count if dx==`i'
       if r(N)>500 {
             regress peak_pra age if dx==`i'
       } 
       else {
             di "There are fewer than 500 cases."
       }
   }
   

9. Define a program called reg_pra. This program will perform the same tasks as described in Question 8, but the regression will take one or more variables specified by the user as the predictor.

   capture program drop reg_pra
   program define reg_pra
       syntax varlist
   
       forvalue i=1/9 {
           qui count if dx==`i'
           if r(N)>500 {
                 regress peak_pra `varlist' if dx==`i'
           } 
           else {
                 di "There are fewer than 500 cases."
           }
         }
   
   end
   

10. You have all your commands in your do file, right? Run your do file from the beginning and make sure your do file does exactly the same thing.

Part II

The lab shared with the students has all the code & solutions. Be sure to clarify anything that remains confusing to them. Hierarchical data are the most poorly taught kind in all school, including in this course :(