|Probit analysis programs|
These programs are used for statistical analysis of data from bioassay studies, such as determining the effects of insecticides on insect mortality. The programs are written in the Mathematica language. You must have the Wolfram Mathematica or Wolfram Player Pro software on your computer to run these programs. Note: to determine whether you have free access to Mathematica, visit the Mathematica web site (www.wolfram.com) and the web site will automatically notify you if you have a site license. If you don't have a site license, the Player Pro software package is more economical to purchase if you will only be using the software to run the probit programs that I have written. Player Pro is not a full implementation of the Mathematica software package, but it will allow you to run programs written in the Mathematica language. If you do not have a site license or do not have the Mathematica or Player Pro software package on your computer, you will not be able to run the programs that I have written.
Note: The programs were updated in June 2013 so that the programs will run in either Wolfram Mathematica 9 or Wolfram Player Pro.
Use the following links to download the programs (zip files). Descriptions of the programs are given below.
Instructions for downloading and installing files
The PROBIT program is used to analyze bioassay data when multiple observations over time were made on the same groups of organisms at one dose of a stimulus. If you made multiple observations over time at more than one dose in a single study, don't use this program to analyze those data. Instead, use the program by Preisler and Robertson (1989. Journal of Economic Entomology 82: 1534-1542). Our program gives you the option of using any of six possible transformations of the data (probit, logit, CLL [complementary log-log], log-probit, log-logit, log-CLL). All information for complete reporting of probit analyses is provided by the program, including: the slopes and intercepts, with their variances and covariance; the chi-square for goodness-of-fit of the regression line; and lethal time values, with confidence limits. The program PROBIT2 does the same thing, but will calculate all six possible transformations at one time.
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.
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.
Instructions for running the programs
Contact Dr. James Throne with questions or comments.
Mention of a proprietary product does not constitute an endorsement or a recommendation for its use by USDA.