Anthony: You can't do it "after the fact." If you want the intercept to be 5 (say), subtract 5 from all of your response (y) values. Then regress these new response values on your predictor (explanatory) variable(s) but using the no intercept (or no constant) option in your regression software.
In the case of a single predictor variable, the formula for the least squares slope is just slope = Sum[(y-5)*x}/Sum[x^2} where I am assuming a fixed intercept of 5. By the way, if you are using Excel you are out of luck. I am told that Excel is not programmed to do least squares with no intercept. Hope this helps. Jon Cryer At 07:55 AM 6/18/2002 -0700, you wrote: >hi, > >thanks for the response. unfortunately, the exact steps are still >unclear to me.. sorry for the trouble. but let's say using the >standard best fit technique i get the slope of 0.5 and intercept of 40 >for a set of data points. how i would like to force the intercept to >be 40.04 and have it best fit the data with this constraint.. what are >the steps i should take? if you can make it unncessarily clear to me >that would be great. thanks in advance. > >anthony > >[EMAIL PROTECTED] (Jay Warner) wrote in message >news:<[EMAIL PROTECTED]>... > > Adjust the response - y function, with a constant, so that the > > expected y > > intercept is 0. then specify as much when you run the regression. > > > > Of course, you will also plot the reslt, and test whether this forced > > intercept makes visual, as well as mathematical and physical, sense. > > > > Cheers, > > Jay > > > > Anthony Yip wrote: > > > > > hi all, > > > > > > this might be a rather silly question. i have a set of data point that > > > i wish to "best fit" however, i would like the y intercept to be > > > constrained to a specific value. does anyone knows the formula or how > > > to do this? is there a matlab function that does this? or anything > > > from "numerical recipes in c" that does it? > > > > > > i have looked and searched the web but couldn't find it.. i know it > > > should be quite basic since its an option in excel to set the > > > y-intercept to a specific value when u best fit a line thru a set of > > > data points.. > > > > > > any help would be greatly appreciated! thanks in advance! > > > > > > p.s. it would be even better if its already programmed in C or > > > equivalent language. :) > > > > > > anthony > > > . > > > . > > > ================================================================= > > > Instructions for joining and leaving this list, remarks about the > > > problem of INAPPROPRIATE MESSAGES, and archives are available at: > > > . http://jse.stat.ncsu.edu/ . > > > ================================================================= > > > > -- > > Jay Warner > > Principal Scientist > > Warner Consulting, Inc. > > 4444 North Green Bay Road > > Racine, WI 53404-1216 > > USA > > > > Ph: (262) 634-9100 > > FAX: (262) 681-1133 > > email: [EMAIL PROTECTED] > > web: http://www.a2q.com > > > > The A2Q Method (tm) -- What do you want to improve today? > > . > > . > > ================================================================= > > Instructions for joining and leaving this list, remarks about the > > problem of INAPPROPRIATE MESSAGES, and archives are available at: > > . http://jse.stat.ncsu.edu/ . > > ================================================================= >.. >.. >================================================================= >Instructions for joining and leaving this list, remarks about the >problem of INAPPROPRIATE MESSAGES, and archives are available at: >.. http://jse.stat.ncsu.edu/ . >================================================================= . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
