[Rd] lower.tail option in pnorm

[Ken Knoblauch]

Hi,

I would have thought that these two constructions would
produce the same result but they do not.

Resp <- rbinom(10, 1, 0.5)
Stim <- rep(0:1, 5)
mm <- model.matrix(~ Stim)
Xb <- mm %*% c(0, 1)
ifelse(Resp, log(pnorm(Xb)), log(1 - pnorm(Xb)))
pnorm(as.vector(Xb), lower.tail = Resp, log.p = TRUE)

> ifelse(Resp, log(pnorm(Xb)), log(1 - pnorm(Xb)))
  [1] -0.6931472 -1.8410216 -0.6931472 -0.1727538 -0.6931472
  [6] -0.1727538 -0.6931472 -1.8410216 -0.6931472 -1.8410216
> pnorm(as.vector(Xb), lower.tail = Resp, log.p = TRUE)
  [1] -0.6931472 -1.8410216 -0.6931472 -1.8410216 -0.6931472
  [6] -1.8410216 -0.6931472 -1.8410216 -0.6931472 -1.8410216

If I have missed something obvious, I would be grateful
to have it pointed out.

> sessionInfo()
R version 2.10.1 beta (2009-12-04 r50668)
i386-apple-darwin9.8.0

locale:
[1] en_US.UTF-8/en_US.UTF-8/C/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods
[7] base

loaded via a namespace (and not attached):
[1] tools_2.10.1

Thanks for any enlightenment.

best,

Ken

-- 
Ken Knoblauch
Inserm U846
Stem-cell and Brain Research Institute
Department of Integrative Neurosciences
18 avenue du Doyen Lépine
69500 Bron
France
tel: +33 (0)4 72 91 34 77
fax: +33 (0)4 72 91 34 61
portable: +33 (0)6 84 10 64 10
http://www.sbri.fr/members/kenneth-knoblauch.html