[R] xyplot: adding pooled regression lines to a paneled type="r" plot

[Michael Friendly]

Consider the following plot that shows separate regression lines ~ age 
for each subject in the Pothoff-Roy Orthodont data,
with separate panels by Sex:

library(nlme)
#plot(Orthodont)
xyplot(distance ~ age|Sex, data=Orthodont, type='r', groups=Subject, 
col=gray(.50),
    main="Individual linear regressions ~ age")

I'd like to also show in each panel the pooled OLS regression line for 
each Sex in the corresponding panel,
generated by the following model:

Ortho.OLS <- lm(distance ~ age * Sex, data=Orthodont)

Sex is a factor, with Male=0, so the coefficients are:
 > coef(Ortho.OLS)
  (Intercept)           age     SexFemale age:SexFemale
   16.3406250     0.7843750     1.0321023    -0.3048295

I anticipate wanting to fit other models to these data, and also 
displaying the model-predicted
regression lines in the same or similar plot, e.g., for a simple linear 
mixed model:

Ortho.MLM <- lme(distance ~ age * Sex, data=Orthodont,
        random = ~ 1 + age | Subject,
        correlation = corAR1 (form = ~ 1 | Subject))

TIA,
-Michael


-- 
Michael Friendly     Email: friendly AT yorku DOT ca 
Professor, Psychology Dept.
York University      Voice: 416 736-5115 x66249 Fax: 416 736-5814
4700 Keele Street    Web:   http://www.datavis.ca
Toronto, ONT  M3J 1P3 CANADA