also available as LogXact PROCs for SAS® Users

Contents

Overview
Features
Examples
User reviews
Brochure PDF
Related Technical Papers
Evaluation and demo copies
Technical Information
Pricing and Order Information

Overview

LogXact is the best software for nonparametric (exact) analysis. It's user interface is easy to use, and the unmatched quality and breadth of exact tests it offers has made this product the essential tool for thousands of statististicians at the world's leading companies, government agencies, and research organizations. With exact methods you can be confident of the integrity of your analysis.

Why Exact Logistic Regression?
Maximum likelihood is the method that almost all statistical software programs use for logistic regression. For small or imbalanced data sets, the maximum likelihood method is often inaccurate, and unreliable. Exact methods will produce reliable answers in these situations. This method yields exact p-values and confidence intervals no matter how small or imbalanced the data, and converges in large samples to the maximum likelihood approach. Exact answers are always preferable.

In 1970, Cox proposed an alternative method of inference based on the exact permutation distribution of sufficient statistics for the regression parameters. This method is known as "exact logistic regression."

This permutation-based method yields reliably accurate p-values and confidence intervals, no matter how small or imbalanced the data set. As sample size grows and/or the data become better balanced and less sparse, the answer produced by the conventional large sample (asymptotic) method will converge to the answer provided by the exact approach.

Cutting-Edge Algorithms
Until recently, exact logistic regression was never seriously considered to be a practical option. The computational difficulties in implementing it are formidable. In 1988, Cytel principals (faculty at Harvard and MIT) C. R. Mehta and N. R. Patel, with K. F. Hirji, published a breakthrough exact logistic algorithm that won the G. W. Snedecor award for the best paper in Biometrics. Cytel Software's algorithms, refined over the last 15 years with support from the National Institutes of Health, have made exact logistic regression not only computationally feasible, but practical, too. Only LogXact incorporates these cutting-edge algorithms. LogXact's combination of power, accuracy, predictability and speed means knowing the correct answer is both possible and practical.

The LogXact 6 software offers completely new regression and multivariate analysis capabilities. For a complete list of new features, please download the LogXact product brochure.

LogXact PROCs for SAS Users
LogXact PROCs work seamlessly in your SAS environment. Simply call up the appropriate exact procedure the same way you would call up any other SAS procedure from within SAS itself. No new software to learn, no clumsy transferring of data from one program to another. Since LogXact PROCs let you perform the entire data analysis within the SAS system, the batch file of SAS commands used in the analysis serves to document each step of the report.

Six sample problems brought to us by practicing statisticians, and their corresponding solution times are shown in the LogXact examples area. Click here to view them.

Download LogXact PROCs brochure

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