Troubleshooting
Problem
I need to estimate the LD50 for a given toxin. Can SPSS Statistics do this?
Resolving The Problem
Yes, SPSS Statistics can provide an estimate of the LD50 in the PROBIT procedure. The LD50 is defined as the dose required to kill 50% of exposed organisms. PROBIT produces estimates of the dose required to kill various percentages from 1-99%, with fiducial confidence intervals where they can be calculated. The values are listed under the column labeled for the dose variable in the section of the output entitled "Confidence Limits for Effective VARNAME" (VARNAME is replaced by the name of the variable).
The PROBIT procedure is in the Regression Option. To access it via the menus, specify Analyze>Regression>Probit. Note that PROBIT is designed for grouped dose-response data, and expects data to be structured in what is sometimes called R-of-N or events/trials format, with one variable holding the number of responses for a given dosage and a second variable holdings the number of trials. For a standard LD50 estimation, you would have these two variables plus a dosage variable, which would be entered as a covariate.
There is an example in the Case Studies (Help>Case Studies>Regression Option>Probit Analysis) that illustrates this, though with a marketing example, so the estimation relates to obtaining a certain percentage response to a marketing campaign rather than killing a certain proportion of organisms, but the math is the same in both cases.
Related Information
Historical Number
53881
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Document Information
Modified date:
16 April 2020
UID
swg21480839