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I'm trying to run a probit analysis -- what are Response Frequency and Total Observed?



I have a binary response variable I'd like to predict using a probit regression model in SPSS. I choose Analyze->Regression->Probit from the menus, and instead of seeing a place for my dependent variable, I see two places to put variables called Response Frequency and Total Observed. What am I supposed to do here to run this analysis?

Resolving The Problem

The PROBIT procedure you're accessing through the menus is designed specifically for grouped dose-response data. The Response Frequency is the number of subjects responding at a given dose and, if specified, level of the single factor optionally allowed in PROBIT, and the Total Observed is the total number of subjects in that group. PROBIT expects data in what we refer to as R of N format (from the command syntax, where Response Frequency is the R, and Total Observed is the N), so you have one case per group of subjects who share the same values on all predictor variables.

To run a more standard probit regression model, we suggest using the newer GENLIN or PLUM procedures. GENLIN, added in Release 15.0, is accessed in the menus via Analyze>Generalized Linear Models>Generalized Linear Models. To specify a probit regression you would select the dependent, choose the option Variable represents binary response or number of events, choose the reference category, and specify that the Link Function is Probit. Specifying a binary response variable results in the Binomial distribution being chosen. Independent variables are specified on the Predictors tab, and the Model tab is used to specify how these are to be used. The default model is an intercept-only model, so you must use the Model tab to specify any other model, not just select predictors.

To access PLUM via the menus, select Analyze>Regression>Ordinal. Click on the Options button and choose the probit option from the link function dropdown to specify a probit model. Predictors are chosen to be factors (categorical) or covariates. A main-effects model involving the chosen predictors is the default. Click on the Location button to specify a different model

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Modified date:
16 April 2020