On Fri, 03 Dec 1999 18:18:21 -0800, [EMAIL PROTECTED] (PBL Powerbase
180) wrote:
> First, I am a molecular biologist and have only taken intro stats
> courses during my undergrad days.
>
> I am trying to find a criterion to use as an objective cutoff to discard
> data from experiments. I use non-linear regression curvefitting, and
> Prism, so I emailed graphpad tech spt. Here is the email, and response:
< snip, Q and "never heard of it"; and noncentrality >
> If anyone has any information how to compute "lambda", I would greatly
> appreciate it (in case it helps, my boss was referring to the antiquated
> (1975) program, BIOPROG, which gives "lambda" values.)
1) For lambda, I think you have to find someone who used that same
program. It is *highly* unlikely that the lambda it used had
anything to do with the noncentrality parameter that you found.
2) There is no such thing as a *valid*, generalizable, "objective
cutoff to discard data from experiments." Some people might say,
"discard" is a word that a scientist would never use. - I have seen
the worth of extremes most neatly in examples from geological-surveys:
where the paydirt, or motherlode, is among the extreme values which do
not fit the others.
One notion of cutoff which has validity might be the observation that
a single point can be so extreme that it makes "non-sense" -- in one
fashion or another -- of a particular *statistical analysis*. For
instance, what is being analyzed in ANOVA is the sums of squares
around means; one value can be so extreme that all the other values
might as well be zero, for all their effect on the tests. However,
you have to comment on the data-point when you set it aside from the
ANOVA; you do not "discard data" from the experiment.
--
Rich Ulrich, [EMAIL PROTECTED]
http://www.pitt.edu/~wpilib/index.html
