Re: Calculation of critical p-, z-, t- and F-values

Barry W Brown <brownbar@xxxxxxxxx> wrote in news:1194973846.237936.54710
@o3g2000hsb.googlegroups.com:

Our free (open source, no charge) software package Stattab calculates
the values for most common statistical distributions (and a few
uncommon ones). Windows and Mac executables available as well as
source.

http://biostatistics.mdanderson.org/SoftwareDownload

M.D. Anderson Cancer Center has a consistent history of making useful
software and statistical advice available on its website. I salute you.

Also, the (free) statistical package R (www.r-project.org) contains
the tables built in; however R has a somewhat steep learning curve.

All one needs to do in R is execute very simple procedures. If you cannot
remember all the distribution functions, all you need to do is type:
help.search("distribution")

Typing qnorm(0.975) will produce the desired quantile of the inverse
Normal. The OP desired a method for "critical values for z,
p, t and F for a significance level (e. g. 99 %)". I don't know what he
meant by "p" but the corresponding values to the t from qt(<quantile>,
<degrees of freedom>) and for the F distribution would be obtained by
typing qf(<quantile>,<df1>,<df2> ).

qt(0.975,60)
[1] 2.000298
qt(0.975,120)

[1] 1.979930
# if you wanted the critical values for 10 through 60 df in steps of 10
this would work:

qt(0.975,seq(10,60,10))
[1] 2.228139 2.085963 2.042272 2.021075 2.008559 2.000298

qt(0.975,Inf)
[1] 1.959964
qnorm(0.975)
[1] 1.959964

You would find that qf(2*p - 1, 1, df)) was identical to qt(p, df)^2).

Not very steep if you ask me. Installation is simple enough for an old doc
to do it without much pain ever since version 1.8.

--
David Winsemius, MD, MPH

.

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