we want to use this model to calculate the X threshold where Y begin to decline, with conidence interval.
The attached is out data.
who has the procedure? could ou send me a copy? thanks a lot.
Carefully look at the documentation for PROC NLIN, especially Example 63.1 Segmented model. This fits a quadratic up to an unknown join point, followed by a plateau.
title 'Quadratic Model with Plateau';
proc nlin data=a;
parms alpha=.45 beta=.05 gamma=-.0025;
x0 = -.5*beta / gamma;
if (x < x0) then
mean = alpha + beta*x + gamma*x*x;
else mean = alpha + beta*x0 + gamma*x0*x0;
model y = mean;
if _obs_=1 and _iter_ =. then do;
plateau =alpha + beta*x0 + gamma*x0*x0;
put / x0= plateau= ;
end;
output out=b predicted=yp;
run;
I hope this gets you started on what you wish to do.
Steve Denham
Thanks so much Steve, and also, does below procedure can also be used for our data? what the difference between this 2 procedures?
DATA a;
INPUT met gain @@;
DATALINES;
80 102 85 115 90 125 95 133 100 140
105 141 110 142 115 140 120 142
;
PROC NLIN;
PARMS a = 102 b = 2.7 c = -0.04;
x = met-80;
x0 = -.5*b / c;
IF x < x0 THEN
MODEL gain = a+b*x+c*x*x;
ELSE
MODEL gain = a+b*x0+c*x0*x0;
IF _obs_=1 and _iter_ =. THEN DO;
plateau = a+b*x0+c*x0*x0;
x0 = x0+80;
PUT / x0 = plateau= ;
END;
RUN;
and another question is, how to make a graph like below, thanks a lot.
Are you ready for the spotlight? We're accepting content ideas for SAS Innovate 2025 to be held May 6-9 in Orlando, FL. The call is open until September 25. Read more here about why you should contribute and what is in it for you!
Learn the difference between classical and Bayesian statistical approaches and see a few PROC examples to perform Bayesian analysis in this video.
Find more tutorials on the SAS Users YouTube channel.