# [Rd] lower.tail option in pnorm

Ken Knoblauch ken.knoblauch at inserm.fr
Tue Dec 8 17:30:59 CET 2009

```Thank you.  That explains it.  I didn't read closely enough.

best,

Ken

Quoting Prof Brian Ripley <ripley at stats.ox.ac.uk>:

> From the help page:
>
>      pnorm(q, mean = 0, sd = 1, lower.tail = TRUE, log.p = FALSE)
>
>      x,q: vector of quantiles.
>
> lower.tail: logical; if TRUE (default), probabilities are P[X <= x],
>           otherwise, P[X > x].
>
> Note that lower.tail is not said to be a vector, and the first value is
> taken (what it is is random in your example).
>
>
> On Tue, 8 Dec 2009, Ken Knoblauch wrote:
>
>> 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
>>
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>
> --
> Brian D. Ripley,                  ripley at stats.ox.ac.uk
> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> University of Oxford,             Tel:  +44 1865 272861 (self)
> 1 South Parks Road,                     +44 1865 272866 (PA)
> Oxford OX1 3TG, UK                Fax:  +44 1865 272595

--
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

```