The "formulas" are actually equations that require iterative solution. They
are covered in many references. My favorite handy paper for MPN's with
dilutions other than 10 is:
Hurley, MA & Roscoe, ME, Automated statistical analysis of microbial
enumeration by dilution series, Journal of Applied Bacteriology 1983, 55,
pp. 159-164 (1983).
It's got a simple BASIC program which you could run on a really old
computer, or convert to something newer.
Some other references are:
Koch, AL. Estimation of the Most Probable Number with a programmable pocket
calculator. Applied & Environmental Microbiology 43, pp. 488-490 (1982)
Cochran, WG. Estimation of Bacterial Density by means of the 'Most Probable
Number'. Biometrics 6, 105-116 (1950)
Finally, the comprehensive one:
Halvorson, HO & Ziegler NR. Application of statistics to problems in
bacteriology. Journal of Bacteriology 25, 101-121 (1933).
Hope this helps,
Alan Hochberg
Qualicon, Inc.
www.qualicon.com
