LD 50 help ,

Mark fuller at envirogen.com
Thu May 14 22:00:41 EST 1998

Chuck Miller wrote:
> Hi Hamdi,
> The BIONET.TOXICOLOGY newsgroup is archived and is searchable. The subject
> of LD50s has come up several times in the past. Try doing a search using
> LD50 as a keyword. Regarding programs to calculate LD50, I am sure some
> exist, although I don't know of any offhand. Most of the commonly used
> graphing programs (SigmaPlot, Cricket Graph, SlideWrite, etc.) can be used
> to do this.
> Best of results,
> Chuck
> Dr. Charles A. Miller, III,   rellim at mailhost.tcs.tulane.edu
> Dept. Environmental Health Sciences, SL29
> Tulane-Xavier Center for Bioenvironmental Research and
> Tulane Univ. School of Public Health and Tropical Medicine
> 1430 Tulane Ave.
> New Orleans, LA 70112
> (504)585-6942, fax (504)584-1726
> Bionet.toxicology newsgroup: http://www.bio.net/hypermail/TOXICOLOGY

The best way I've found is to normalize your response data to 100%, then
fit a logistic curve to the data.  The inflection point is the 50%
reduction or 50% death or 50% inhibition level, depending on what your
system is testing.  I use KaleidaGraph, whicd allows you to define the
curve fitting equation, which may need "massaging" at times.

Please see my paper--

M. E. Fuller and K. M. Scow. 1996. Effects of toluene on
microbially-mediated processes involved in the soil nitrogen cycle.
Microbial Ecology 32(2): 171-184.

for more details.


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