package "rms" nomogram
Putting context back in.
On Jul 31, 2012, at 9:01 AM, B787s wrote:
Dear R-Help, I am using 'rms' package to draw nomogram. I wonder how is the "Points" determined for each predictor in the model? Is it by the coefficient estimate (beta) relative to the highest effect in the model or?
It would be better if you asked this question about a specific example because the rms package has many sorts of regression fit- objects for which nomogram will provide results. The linear predictor in a regression method will have contributions from each of the terms, so I would have said that the variate scales were being displayed relative to the mean values rather than relative to the "highest effect" ... what ever that term means to you. The upper portion of a nomogram is used to calculate "Points", while the lower portion is used to calculate probability of event by transforming from the linear predictor scale to the response scale. A unit-increment in "Points" displayed by 'plot.nomogram' for one variate will be related to a unit increment of another variate by the ratios of their coefficients.
Thanks Lin
David Winsemius, MD
On Aug 1, 2012, at 6:22 PM, B787s wrote:
Thanks, it is helpful. I knew there were several modeling capacities built into this package "rms". I would just like to have a general ideal how the points for each predictor determined. I read a paper by Lasonos et al 2008. It mentioned it was by the size of the effect.
Let me guess.... it's the one lying behind the request for US$ at: http://jco.ascopubs.org/content/26/8/1364.long It seems possible the conceptual gaps may be in the degree to which you understand how glm() functions work. Do you have a working understanding of what a linear predictor is? Do you understand what a link function does? Do you understand that a unit change in the linear predictor will not imply a unit change in the response unless the link function is "identity"? If the article did not cover those topics then you were ill-served.
David Winsemius, MD Alameda, CA, USA