User error in calling predict/model.frame
On Sat, Jan 29, 2011 at 1:23 PM, Joshua Wiley <jwiley.psych at gmail.com> wrote:
xxAB <- dat$xxA * dat$xxB meanAB <- meanA * meanB sdAB <- sqrt(sdA^2 + sdB^2 + meanA^2 * sdB^2 + meanB^2 * sdA^2)
don't know why I did that the hard way (besides I think I messed up the formula slightly), but the point is there's still a difference between the scaled interaction from unscaled variables and the interaction of scaled variables. sdAB <- sd(xxAB) # <-- what I should have done
(xxAB - meanAB)/sdAB
[1] 0.18412267 -0.97105894 -1.45088077 -1.37131900 0.09339332 0.74663645 [7] -1.27092403 -0.41183471 -1.45890639 0.06568750 0.60130106 1.35945072 [13] 0.79255938 1.80314145 0.51553234 -0.23553700 -0.42045914 -0.73543976 [19] 1.40009474 0.68251640
(sxxAB <- with(dat, scale(xxA) * scale(xxB))[1:20,])
?[1] ?0.01838999 ?0.25899229 -0.15337178 ?1.07536361 -0.26520706 ?0.25119036 ?[7] -0.11295999 ?0.05205466 -1.49676116 -0.14367368 -1.86921225 ?0.80860167 [13] -0.44816896 ?1.44122535 -0.73361472 -0.14930187 -1.46192081 ?0.19784309 [19] ?0.62089372 ?0.0821291515