Comparing Points on Two Regression Lines

What I need is to compare these predicted values on both lines:

predict(m1, newdata = data.frame(x = x))

        1        2        3        4        5
84.42477 84.26280 81.34729 60.29085 27.89632

predict(m2, newdata = data.frame(x = x))

        1        2        3        4        5
76.86037 76.69170 73.65554 51.72772 17.99261

for example: compare 84.42477  versus 76.86037 , and   84.26280  versus  76.69170  and so on.




with many thanks
abou




==========================
AbouEl-Makarim Aboueissa, Ph.D.
Associate Professor of Statistics
Graduate Program Coordinator
Department of Mathematics&  Statistics
University of Southern Maine
96 Falmouth Street
P.O. Box 9300
Portland, ME 04104-9300
USA


Tel: (207) 228-8389
Fax: (207) 780-5607
Email: aaboueissa at usm.maine.edu
           aboueiss at yahoo.com

Office: 301C Payson Smith

"R. Michael Weylandt"<michael.weylandt at gmail.com>  3/31/2012 9:13 PM>>>

Again, you need to clarify what you mean by compare, but here's a
better way to do predict from a linear model -- my first guess was
simple interpolation (not very good):

m1<- lm(y ~ x, data = data.frame(y = y1, x = x1))
m2<- lm(y ~ x, data = data.frame(y = y2, x = x2))

predict(m1, newdata = data.frame(x = x))
predict(m2, newdata = data.frame(x = x))

Perhaps you want an ANOVA (?anova) test to compare the models: if you
want to compare the predicted values at x directly, you could use
interval="predict" for the different models and see if they overlap at
a given confidence level.

Michael

PS -- Please do cc the list: I'm not a statistics expert by any means
and I'd hate for what I say to go unreviewed by actual experts.

On Sat, Mar 31, 2012 at 8:19 PM, AbouEl-Makarim Aboueissa
<aaboueissa at usm.maine.edu>  wrote:

I need to compare the value of y1-hat versus y2-hat corresponding to these
values of x<-c(0.10,0.20,2.0,15.0,35.0)
e.g. for x=0.10 compare y1-hat(x=0.10) versus y2-hat(x=0.10) and so on.

thanks
abou

"R. Michael Weylandt"<michael.weylandt at gmail.com>  3/31/2012 8:10 PM>>>

? approxfun

f1<- approxfun(x1,y1)
f2<- approxfun(x2,y2)

f1(x) - f2(x)

But I'm not sure what you mean be compare...do you have a particular
test in mind?

Michael

On Sat, Mar 31, 2012 at 8:04 PM, AbouEl-Makarim Aboueissa
<aaboueissa at usm.maine.edu>  wrote:

Dear All:

I am trying to compare points on two regression lines given some specific
values of X. I am not sure how to do it in R and/or in SAS. Can someone help
me, and show me how to conduct such test in R.


You can use the following data for both lines.

### data for line 1:
### =========

x1<-c(0.0,0.25,2.5,25.0,50.0)
y1<-c(100.0,79.0,74.0,36.0,8.0)



### data for line 2:
### =========

x2<-c(0.0,0.25,2.5,25.0,50.0)
y2<-c(100.0,79.0,55.0,18.0,2.0)


### these are the given values of X:
###  ===================

x<-c(0.10,0.20,2.0,15.0,35.0)


thank you very much in advance
abou








==========================
AbouEl-Makarim Aboueissa, Ph.D.
Associate Professor of Statistics
Graduate Program Coordinator
Department of Mathematics&  Statistics
University of Southern Maine
96 Falmouth Street
P.O. Box 9300
Portland, ME 04104-9300
USA


Tel: (207) 228-8389
Fax: (207) 780-5607
Email: aaboueissa at usm.maine.edu
          aboueiss at yahoo.com

Office: 301C Payson Smith


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