Re: [S] correlation coefficient from nls
Dave Krantz (dhk@paradox.psych.columbia.edu)
Mon, 27 Apr 1998 07:28:59 -0400
A value of r^2 always is based (explicitly or implicitly) on a
comparison of two models, usually nested in the sense that the
model with fewer parameters can be viewed as a specialization
of the model with more parameters. The value of r^2 is then
1 minus the ratio of the smaller to the larger sum of squared
residuals. Thus, there is no such thing as the r^2 from a single
fitted model--one must always think about what model (perhaps an
implicit "null" model) is held out as a standard of comparison.
Once that is determined, the calculation is straightforward, based
on the sums of squared residuals from the two models. This is
particularly appropriate for nls(), which minimizes a sum of squares.
Dave Krantz
-----------------------------------------------------------------------
This message was distributed by s-news@wubios.wustl.edu. To unsubscribe
send e-mail to s-news-request@wubios.wustl.edu with the BODY of the
message: unsubscribe s-news