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esraa1
Fluorite | Level 6
hi!
I have a data ( number of crashes ). I used interrupted time series to show the effect of speed camera that introduced at time=49
I want to plot in one graph as in the Figure1a in the link http://www.cdc.gov/pcd/issues/2013/12_0268.htm

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shayma
1 ACCEPTED SOLUTION

Accepted Solutions
GraphGuy
Meteorite | Level 14

Here's one "brute force" way to do it (somebody might come up with a more elegant way to do it). It produces the following plot:

 

broken.png

 

data my_data;
format time comma8.0 value comma8.0;
input value time;
if time <=43 then series1=value;
else series2=value;
datalines;
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;
run;

 

proc reg data=my_data plots=none noprint;
model series1 = time;
output out=my_data p=series1_predicted;
run;

 

proc reg data=my_data plots=none noprint;
model series2 = time;
output out=my_data p=series2_predicted;
run;

 

data my_data; set my_data;
if time<=43 then series2_predicted=.;
run;

 

title1 height=16pt "Custom Broken/Piecewise Regression Plot";

 

proc sgplot data=my_data;
label value='Smoking Rate';
label series1_predicted='Trend without tax increase';
label series2_predicted='Trend with tax increase';
series x=time y=value / lineattrs=(color=black)
markers markerattrs=(size=6px color=black symbol=circlefilled);
series x=time y=series1_predicted / lineattrs=(color=black pattern=shortdash);
series x=time y=series2_predicted / lineattrs=(color=black pattern=dash);
yaxis label="Percentage";
xaxis display=(nolabel);
keylegend / across=1 position=bottomright location=inside
linelength=35px border valueattrs=(size=11pt);
run;

 

 

View solution in original post

13 REPLIES 13
Rick_SAS
SAS Super FREQ

I am not sure what question you are asking. You can use PROC SGPLOT to create the plot of NumCrashes vs Time:

 

proc sgplot data=Have;
  series y=NumCrashes x=Time / markers;
run;

SGPlot4.png 

esraa1
Fluorite | Level 6

thank you 

 I used intervention analysis. so, i need to plot a graph similar to the  picture below.

esraa1_0-1584701853950.png

 

shayma
Rick_SAS
SAS Super FREQ

OK, so add the two fit lines to the data set that has the data. Use a binary indicator variable to specify which predicted values are for the pre/post model. Then add another SERIES statement, like this

series x=Time y=Predicted / group=PrePost;

For example:

proc sort data=Sashelp.Class out=Have;
by Height;
run;

data Pred;
input PrePost Height Predicted;
datalines;
1 51  56
1 72 150
2 64 110
2 72 100
;

data All;
set Have Pred;
run;

proc sgplot data=All;
series x=Height y=Weight;
series x=Height y=Predicted / group=PrePost;
run;
esraa1
Fluorite | Level 6

ok, I need the regression lines in the graph!

esraa1_0-1584712543177.png

 

shayma
Rick_SAS
SAS Super FREQ

Do you have the regression lines or not? In your original post you said "I used interrupted time series to show the effect of ...," which sounds like you already have the regression line.

 

If you want OLS lines for each segment, you can use 

REG x=Time y=NumCrashes / group=PrePost;

Be aware, however, that those are least squares regression lines. If you want something more sophisticated, fit a model to the data and use the OUTPUT statement to output the predicted values to a SAS data set, then use my earlier method.

 

esraa1
Fluorite | Level 6

i used this code 

proc sgplot data=FitOut;
scatter x=time y=crashes / group=group;
series x=time y=crashes/ group=group;
reg x=time y=crashes/ group=group;
run;

 

and the result as show below. I used linear regression and I have the equation of the regression but I want to show the regression lines in the graph in two period ( before and after ) 

 

esraa1_0-1584715327670.png

 

shayma
Rick_SAS
SAS Super FREQ

Notice the PROC SORT at the top of my example. Try this:

proc sort data=FitOut;
by group time;
run;

proc sgplot data=FitOut;
series x=time y=crashes/ group=group markers;  
reg x=time y=crashes/ group=group nomarkers;
run;

 

esraa1
Fluorite | Level 6

Thank you, this what i asked for 

esraa1_0-1584712259645.png

if possible, I want to delete the regression line for the first period and make it for all period (1-66) .how?  

shayma
esraa1
Fluorite | Level 6

esraa1_0-1584714373106.png

 

shayma
GraphGuy
Meteorite | Level 14

Here's one "brute force" way to do it (somebody might come up with a more elegant way to do it). It produces the following plot:

 

broken.png

 

data my_data;
format time comma8.0 value comma8.0;
input value time;
if time <=43 then series1=value;
else series2=value;
datalines;
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;
run;

 

proc reg data=my_data plots=none noprint;
model series1 = time;
output out=my_data p=series1_predicted;
run;

 

proc reg data=my_data plots=none noprint;
model series2 = time;
output out=my_data p=series2_predicted;
run;

 

data my_data; set my_data;
if time<=43 then series2_predicted=.;
run;

 

title1 height=16pt "Custom Broken/Piecewise Regression Plot";

 

proc sgplot data=my_data;
label value='Smoking Rate';
label series1_predicted='Trend without tax increase';
label series2_predicted='Trend with tax increase';
series x=time y=value / lineattrs=(color=black)
markers markerattrs=(size=6px color=black symbol=circlefilled);
series x=time y=series1_predicted / lineattrs=(color=black pattern=shortdash);
series x=time y=series2_predicted / lineattrs=(color=black pattern=dash);
yaxis label="Percentage";
xaxis display=(nolabel);
keylegend / across=1 position=bottomright location=inside
linelength=35px border valueattrs=(size=11pt);
run;

 

 

esraa1
Fluorite | Level 6

@GraphGuy  thank you, you are right, this is a Piecewise Regression 

but how can get the coefficients (regression equation ) for the Piecewise Regression and R square  by sas ?

shayma
Rick_SAS
SAS Super FREQ

I believe we have answered your questions about how to create a graph. If you want to learn more about regression in SAS, you might want to open a separate thread in the Statistical Procedures Community.

 

All of your questions can be answered by a Google search or by reading the SAS documentation (especially the Getting Started examples) for PROC GLM. There are many blog posts about regression models that change at a cutpoint.

There are also papers about piecewise linear models.Keywords are

+SAS piecewise linear regression model

 

Good luck with your project.

esraa1
Fluorite | Level 6

 useful links.I got what I want 

thank you

shayma

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