[R] A "rude" question

[Paul Gilbert]

One point that did not get mentioned in this discussion, and I believe 
deserves
much more publicity, is the impact of packages tests. The design of the 
package
 system allows package developers to put tests in packages, and these 
are checked
regularly (see <http://cran.at.r-project.org/contrib/checkSummary.html>).

These are intended to test the package functionality, but also give R 
what is
perhaps the largest test suite of any statistical software (certainly 
the most
quickly growing). While any single package's test will never guarantee that
the package works perfectly, the ensemble goes a long way toward ensuring
that core R functionality behaves as intended. It seems unlikely to me 
that any
commercial effort will ever be able to catch up.

There are several ways that tests can add to our confidence that 
calculations 
can be trusted. They can
   - check against theoretical results
   - check against published results
   - check against results from other software
   - check that calculations done in different ways give the same result
   - check that monte carlo experiments give distributions that are 
consistent
      with expected results

Some of these are relatively time consuming to set up and check the 
first time,
but after that they can be automatic.

If you have particular calculations with specific packages that you are 
especially
concerned about, I encourage you to participate by devising good tests 
and sending
them to the package developers. (But first check the tests they are 
already doing
in the package tests directory.)

Paul Gilbert

msck9 at mizzou.edu wrote:

>Dear all, 
> I am beginner using R. I have a question about it. When you use it,
> since it is written by so many authors, how do you know that the
> results are trustable?(I don't want to affend anyone, also I trust
> people). But I think this should be a question.
>
> Thanks,
> Ming
>
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