Example of a Logistic Report
The logistic probability plot gives a complete picture of what the logistic model is fitting. At each x value, the probability scale in the y direction is divided up (partitioned) into probabilities for each response category. The probabilities are measured as the vertical distance between the curves, with the total across all Y category probabilities summing to 1.
Related Information
 • Additional Example of a Logistic Plot
The Whole Model Test report shows if the model fits better than constant response probabilities. This report is analogous to the Analysis of Variance report for a continuous response model. It is a specific likelihood-ratio Chi-square test that evaluates how well the categorical model fits the data. The negative sum of natural logs of the observed probabilities is called the negative log-likelihood (–LogLikelihood). The negative log-likelihood for categorical data plays the same role as sums of squares in continuous data. Twice the difference in the negative log-likelihood from the model fitted by the data and the model with equal probabilities is a Chi-square statistic. This test statistic examines the hypothesis that the x variable has no effect on the responses.
Values of the Rsquare (U) (sometimes denoted as R2) range from 0 to 1. High R2 values are indicative of a good model fit, and are rare in categorical models.
 • The Reduced model only contains an intercept.
 • The Full model contains all of the effects as well as the intercept.
 • The Difference is the difference of the log likelihoods of the full and reduced models.
Measures variation, sometimes called uncertainty, in the sample.
Full (the full model) is the negative log-likelihood (or uncertainty) calculated after fitting the model. The fitting process involves predicting response rates with a linear model and a logistic response function. This value is minimized by the fitting process.
Reduced (the reduced model) is the negative log-likelihood (or uncertainty) for the case when the probabilities are estimated by fixed background rates. This is the background uncertainty when the model has no effects.
The likelihood-ratio Chi-square test of the hypothesis that the model fits no better than fixed response rates across the whole sample. It is twice the –LogLikelihood for the Difference Model. It is two times the difference of two negative log-likelihoods, one with whole-population response probabilities and one with each-population response rates.
The observed significance probability, often called the p value, for the Chi-square test. It is the probability of getting, by chance alone, a Chi-square value greater than the one computed. Models are often judged significant if this probability is below 0.05.
 • the log-likelihood from the fitted model
 • the log-likelihood from the model that uses horizontal lines
The total sample size used in computations. If you specified a Weight variable, this is the sum of the weights.
The nominal logistic model fits a parameter for the intercept and slope for each of logistic comparisons, where k is the number of response levels. The Parameter Estimates report lists these estimates. Each parameter estimate can be examined and tested individually, although this is seldom of much interest.
 Term Lists each parameter in the logistic model. There is an intercept and a slope term for the factor at each level of the response variable, except the last level. Estimate Lists the parameter estimates given by the logistic model. Std Error Lists the standard error of each parameter estimate. They are used to compute the statistical tests that compare each term to zero. Chi-Square Prob>ChiSq Lists the observed significance probabilities for the Chi-square tests.