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United States Department of Agriculture

Agricultural Research Service

Probit Software
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Not sure which program you need for probit analysis?

If you treated one batch of organisms with one dose of a stimulus (e.g., a pesticide or drug) and looked at response (e.g., mortality) of that one batch of organisms several times after exposure, click here for time-mortality analysis of correlated data. (E.g., you treated one batch of 100 insects with one dose of an insecticide, and then checked mortality of that one batch of insects at 24, 48, 72, 96, and 120 h.)

If you treated several batches of organisms with one dose of a stimulus (e.g., a pesticide or drug) and at a series of times looked at response (e.g., mortality) of one of those batches of organisms, click here for time-mortality analysis of independent data. (E.g., you treated 5 batches of 100 insects with one dose of an insecticide, and then checked mortality of 1 batch at 24 h, another batch at 48 h, another batch at 72 h, another batch at 96 h, and another batch at 120 h.)

If you treated several batches of organisms with different doses of a stimulus (e.g., a pesticide or drug) and looked at response (e.g., mortality) after a fixed period of time, click here for dose- mortality analysis of independent data. (E.g., you treated 5 batches of 100 insects with 10, 20, 30, 40, and 50 ppm of an insecticide, and then checked mortality at 24 h.)

Additional utilities are available below, but use of these utilities requires that you have access to the Mathematica software program. Note: To determine whether you have free access to Mathematica, visit the Mathematica web site (www.mathematica.com) and the web site will automatically notify you if you have a site license. If you do not have a site license or do not have the Mathematica software package on your computer, you will not be able to run the programs that I have written.

Papers describing the techniques used:
 pdf icon PDF   Throne, J. E., Weaver, D. K., Chew, V., and Baker, J. E. 1995. Probit analysis of correlated data: Multiple observations over time at one concentration. J. Econ. Entomol. 88: 1510-1512.
 pdf icon PDF   Throne, J. E., Weaver, D. K., and Baker, J. E. 1995. Probit analysis: Assessing goodness-of-fit based on backtransformation and residuals. J. Econ. Entomol. 88: 1513-1516.

Backtransformation programs

The backtransformation programs use output from the PROBIT program, or from any other probit analysis program. The BACKTRAN program can be used to transform probit-, logit-, or CLL-transformed data back to the original units (proportion organisms responding to the stimulus) to help assess goodness of fit. The program will also calculate residuals and standardized residuals of proportion organisms responding to the stimulus. The program outputs time or dose, the observed and predicted proportion organisms responding at each time or dose, and the residual and standardized residual corresponding to each time or dose. The program also outputs the observed and predicted probit-transformed (or logit- or CLL-transformed) data corresponding to each time or dose. These data can be used to plot observed vs. predicted proportion organisms responding to the stimulus, or the corresponding probits, to assess goodness-of-fit. These graphs are also automatically generated by the BACKTRAN program. BACKTRAN should be used only for data that are correlated - i.e., you looked at the same insects over several time periods. If your data consist of independent observations - i.e., a different batch of organisms for every observation time or for each dose - use BACKTRN2.
Download Backtransformation programs here

Accessory programs

The accessory programs use output from the PROBIT program, or from any other probit analysis program. The SLOPE program is used to calculate whether slopes and intercepts from two regression lines differ. The RELPOT program is used to calculate relative potency of two stimuli, including confidence limits on relative potency.
Download Accessory programs here


Contact Dr. James Throne with questions or comments.

Last Modified: 2/24/2014