This section describes how predicted probabilities and confidence limits are calculated by using the maximum likelihood estimates (MLEs) obtained from PROC LOGISTIC. For a specific example, see the section Getting Started: LOGISTIC Procedure. Predicted probabilities and confidence limits can be output to a data set with the OUTPUT statement.
For a vector of explanatory variables , the linear predictor
is estimated by
where and are the MLEs of and . The estimated standard error of is , which can be computed as the square root of the quadratic form , where is the estimated covariance matrix of the parameter estimates. The asymptotic confidence interval for is given by
where is the th percentile point of a standard normal distribution.
The predicted probability and the confidence limits for are obtained by backtransforming the corresponding measures for the linear predictor, as shown in the following table:
Link 
Predicted Probability 
100(1–)% Confidence Limits 

LOGIT 


PROBIT 


CLOGLOG 


The CONTRAST statement also enables you to estimate the exponentiated contrast, . The corresponding standard error is , and the confidence limits are computed by exponentiating those for the linear predictor: .
For a vector of explanatory variables , define the linear predictors , and let denote the probability of obtaining the response value i:
By the delta method,
A 100(1)% confidence level for is given by
where is the estimated expected probability of response i, and is obtained by evaluating at .
Note that the contrast and exponentiated contrast , their standard errors, and their confidence intervals are computed in the same fashion as for the cumulative response models, replacing with .