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

[Michael Friendly]

Thanks, Deepayan

I read your presentation and understand how this works for the case you 
presented, but I can't
get it to work for my case, where I want to superimpose model fitted 
lines over individual
subject regression lines.  Here's what I tried

library(nlme)
library(lattice)

## ------------------
## pooled OLS model
## ------------------

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

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

grid <- expand.grid(age=8:14, Sex=c("Male", "Female"))

fm.OLS <-cbind(grid, distance = predict(Ortho.OLS, newdata = grid))

Ortho <-Orthodont[c("age", "Sex", "distance")]
combined <- make.groups(original = Ortho,
                            OLS = fm.OLS)
str(combined)
xyplot(distance ~ age|Sex, data=combined, groups=which, col="black", lwd=2,
  type = c("r", "l"), distribute.type = TRUE
    )

This last just gives me the pooled within-Sex regression lines, which is 
what I want to overlay
on the first plot.

Further, if I try a mixed model, I get errors trying to get the 
predicted values in a similar form

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

fm.MLM <-cbind(grid, distance = predict(Ortho.MLM, newdata = grid))

 > fm.MLM <-cbind(grid, distance = predict(Ortho.MLM, newdata = grid))
Error in predict.lme(Ortho.MLM, newdata = grid) :
  Cannot evaluate groups for desired levels on "newdata"
 >

Deepayan Sarkar wrote:
> On Tue, Jun 22, 2010 at 9:30 AM, Michael Friendly <friendly at yorku.ca> wrote:
>   
>> 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))
>>     
>
> Have a look at
>
> http://user2007.org/program/presentations/sarkar.pdf
>
> -Deepayan
>   


-- 
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