topic Re: Difference-in difference trends plot in Statistical Procedures

Difference-in difference trends plot

sks521 — Tue, 02 Jul 2019 11:06:27 GMT

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

Re: Difference-in difference trends plot

Rick_SAS — Tue, 02 Jul 2019 12:16:57 GMT

1. Please post example data

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

Re: Difference-in difference trends plot

sks521 — Tue, 02 Jul 2019 12:29:24 GMT

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

Re: Difference-in difference trends plot

sks521 — Wed, 03 Jul 2019 08:41:02 GMT

Hi Rick,

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

Thanks