> For example, pt(-1, Inf) = 0.5 in S-Plus 6.1, but 0.159 in
> R; clearly,
> S-Plus gives a wrong answer without warning.
I wasn't aware of this issue. However, for large, non-infinite values of df pt
does give a sensible answer; it's only for the pathological case that it fails.
Nonetheless, I have asked for this issue to be fixed for the next version.
If you're aware of any other areas where the distribution functions have
problems, please do let me know.
# David
--
David M Smith <dsmith@insightful.com>
Product Manager, Insightful Corp, Seattle WA
Tel: +1 (206) 802 2360
Fax: +1 (206) 283 6310
Insightful Corporation (www.insightful.com) provides analytical solutions for
text and data using S-PLUS, Insightful Miner, InFact and consulting services.
> -----Original Message-----
> From: Spencer Graves [mailto:spencer.graves@PDF.COM]
> Sent: Thursday, February 13, 2003 9:12 AM
> To: Jose María Fedriani Laffitte
> Cc: s-news@lists.biostat.wustl.edu
> Subject: Re: [S] Exact p-values
>
>
>
> Try ( 1-pchisq(29.8, df=1)): With S-Plus 6.1, I got 4.78992e-008.
>
> By the way, the distribtion functions in R have more
> arguments.
> For example, pchisq(29.8, df=1, lower.tail=F) produces the same
> answer, and pchisq(29.8, df=1, lower.tail=F, log=T) produces
> its natural
> logarithm. Also, pchisq, dchisq, qchisq, and rchisq in R all have an
> "ncp" noncentrality parameter argument; only pchisq has such
> in S-Plus
> 6.1. Similarly, none of the Student's t functions in S-Plus have a
> non-centralitity parameter; in R, pt has an argument ncp,
> and from this
> one can easily program ncp for dt, qt and rt. Also, the distribution
> functions in the current release of S-Plus are known to have
> problems.
> For example, pt(-1, Inf) = 0.5 in S-Plus 6.1, but 0.159 in
> R; clearly,
> S-Plus gives a wrong answer without warning.
>
> Best Wishes,
> Spencer Graves
>
> Jose María Fedriani Laffitte wrote:
>
> >Dear all,
> >
> > I want to get the exact p-values, on 1 degree of
> freedom, for an array
> >of chi-square values. When my chi-square values are equal
> or lower than
> >29.7, I get the exact associated p-values. Thus, for instance:
> >
> >
> >
> >>pchisq(29.7, df=1)
> >>
> >>
> >[1] 0.9999999
> >
> >However, when my chi-square values are greater or equal to
> 29.8 what I get
> >is:
> >
> >
> >
> >>pchisq(29.8, df=1)
> >>
> >>
> >[1] 1
> >
> >
> > Could anyone tell me how to fix this trivial issue?
> Very grateful, Jose
> >M. Fedriani
> >
> >****************************************
> >Jose Mª Fedriani Laffitte
> >Estacion Biologica de Donana (CSIC)
> >Avda. Mª Luisa s/n
> >41013-Sevilla
> >Spain
> >Tel. +34-954232340
> >Fax +34-954621125
> >http://ebd.csic.es
> >
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