Difference-in difference trends plot

[sks521]

Hi folks,

I wanna do a difference-in differences analysis using proc mixed. The outcome I am regressing on is number of health visits per participant pre-intervention vs. post-intervention between two groups. I have three time points; pre-intervention (12 months), intervention (6 months) and post-intervention (12 months) and I wanna plot average visits per participant (as each participants can have multiple visits in a month) in each month for both intervention and control group.

Does anyone has an example syntax please?

Thanks

S

[Rick_SAS]

1. Please post example data

2. Are you asking for syntax for PROC MIXED, or are you asking for syntax for PROC SGPLOT?

[sks521]

Hi,

Here is example data:

ID    Age    Sex    Practice     Status                   VisitDate        

1      73      M       SMP          Intervention           2016-04-14

1      73      M       SMP          Intervention           2017-02-19

1      73      M       SMP          Intervention           2017-04-16

1      73      M       SMP          Intervention           2016-07-18

2      79      F        BMP          Eligible                  2016-03-11

2      79      F        BMP          Eligible                  2016-08-14

2      79      F        BMP          Eligible                  2018-04-16

2      79      F        BMP          Eligible                  2017-09-21

2      79      F        BMP          Eligible                  2017-03-20

2      79      F        BMP          Eligible                  2018-05-12

Just to let you know that there are other variables like ethnicity etc. which I have not mentioned here.

So I am trying to do a difference in differences to assess change in the number of health visits between the two groups after intervention (intervention was implemented from September 2017 to February 2018). I though I will create dummy variables to create 4 three months intervals for pre-intervention, one for intervention and 4 3 months intervals for post-intervention period and plot the average number of visits per patient per time-period. 

I wasn't sure how to create the plot with counterfactual (usual difference in differences plot). If there is any commant to use in proc mixed, I am happy to use it. Otherwise any suggestion will be much appreciated.

Thanks 

S

[sks521]

Hi Rick,

Would you mind looking at my example data set and post example syntax please?

Thanks

S