interrupted time series

[esraa1]

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 

30 1 
26 2
39 3 
44 4 
35 5     
20 6 
27 7 
67 8 
25 9 
39 10 
69 11   
74 12 
45 13 
41 14 
50 15 
67 16 
55 17   
77 18 
41 19 
38 20
38 21 
46 22 
45 23   
62 24  
60 25  
62 26 
49 27 
60 28
78 29         
69 30      
64 31 
86 32
68 33 
53 34 
59 35 
56 36 
68 37 
57 38 
59 39 
101 40 
63 41
90 42 
92 43 
64 44      
77 45 
69 46
82 47 
70 48 
63 49 
66 50  
78 51 
94 52 
88 53 
62 54 
77 55 
92 56 
76 57 
55 58 
70 59 
54 60 
76 61 
58 62 
58 63
79 64 
77 65 
79 66 
;

[Rick_SAS]

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;

 

[esraa1]

thank you 

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

[Rick_SAS]

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]

ok, I need the regression lines in the graph!

[Rick_SAS]

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]

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 ) 

[Rick_SAS]

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]

Thank you, this what i asked for 

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

[esraa1]

[GraphGuy · Accepted solution]

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:

data my_data;
format time comma8.0 value comma8.0;
input value time;
if time <=43 then series1=value;
else series2=value;
datalines;
30 1
26 2
39 3
44 4
35 5
20 6
27 7
67 8
25 9
39 10
69 11
74 12
45 13
41 14
50 15
67 16
55 17
77 18
41 19
38 20
38 21
46 22
45 23
62 24
60 25
62 26
49 27
60 28
78 29
69 30
64 31
86 32
68 33
53 34
59 35
56 36
68 37
57 38
59 39

101 40
63 41
90 42
92 43
64 44
77 45
69 46
82 47
70 48
63 49
66 50
78 51
94 52
88 53
62 54
77 55
92 56
76 57
55 58
70 59
54 60
76 61
58 62
58 63
79 64
77 65
79 66
;
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]

@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 ?

[Rick_SAS]

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]

 useful links.I got what I want 

thank you