plate count statistics

Charles N Haas haascn at dunx1.ocs.drexel.edu
Sun Nov 26 08:08:42 EST 1995

Bio Techniques Laboratories (cobactin at halcyon.com) wrote:
: In recent years I have found two editorials on the "correct" method to 
: statistically analyze plate count data.  The first one said that the mean 
: and the std. dev. should be determined from the arithmetic values of the 
: data.  The second one said the data should be transformed to logs and 
: then the mean and std. dev. should be calculated and then retransformed 
: to scientific notation.  Are there any more opinions on how to deal with 
: plate count data?  If anyone could suggest a text or article that deals 
: with statistics for the analysis of plate count data, I would appreciate it.
: Thank you!

If plate count data are in control, then the counts should be Poisson
distributed.  To compute the density, sum the total colonies by the total
volumes plated.

The log transformation is one way to approximately transform Poisson
variates into normal variates.  There is a long literature on this, although
some of it is fairly old.  You do not indicate what your overall objective
is, so it is hard to go further.  But if this thread continues, I will put
in a few references of mine that I have written regarding statistical
analysis of microbial data (mostly in the context of disinfection
experiments, however it is equally applicable to growth curve

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