LD50/LD90 Software?

Dirk Bornemeier bornemd at aa.wl.com
Wed Dec 1 13:48:28 EST 1993

In article <mjcoyne-011293095650 at>,
mjcoyne at warren.med.harvard.edu (Michael Coyne) wrote:

> Looking for software for estimating LD50 and LD90 by logit analysis. 
> Possible reference, Acharya AS etal., Comput Methods Programs Biomed
> 34(4):255,1991.  Any ideas or suggestions?
> Thanks...
> Mike

I don't know of software written specifically for this application, but I
can suggest two "work arounds" both of which I've used.

1) You can use a spreadsheet to apply the logit function to your x and y
data (sorry I don't remember the formula for the function off the top of my
head) and then do a linear regression on the results.  You can then use the
equation for this line to back-calculate the x values that correspond to
the y values 50 and 90.  Disclaimer: I'm not a biostatistician so I can't
say what effect  this tranformation has on correlation coefficients, error
estimates, etc., but it definitely works fo calculating the values

2) Use a program that does general curve fitting using either preprogrammed
or user-entered formulas.  EnzFitter, Sigmaplot, and KaleidaGraph are some
of the ones I know of that do this.  After fitting the data you may still
have to back-calculate as descibed above or the program may do it for you.

Hope this helps.

Dirk Bornemeier
Ann Arbor, MI

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