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What is XPro?

XPro is the first software package to employ exact parametric statistical methods as presented in "Exact Statistical Methods for Data Analysis" by Dr. S. Weerahandi, other recent publications, and ASA courses and sessions. Traditional tests and confidence intervals provided by all-purpose statistical software are based on unreasonable assumptions or are approximate methods that were developed prior to the computer age. Therefore, for the sake of computational simplicity, most statistical packages were designed to rely on outdated approximate methods that can introduce unnecessary risks into decisions.

Based on 'exact' methods and the power of current computer technologies, XPro software is able to detect significant and nonsignificant experimental results even with small sample sizes. XPro is used by commercial, academic and government statisticians to perform the most powerful parametric statistical inference in applications such as Regression, ANOVA Fixed/Mixed Effects Models, Repeated Measures Models, and Growth Curve Models.

The latest release of XPro, Version 5 ,introduces a plotting utility to further improve user productivity.

Download XPro Demo Version.

Software to Maximize Research Productivity

XPro has successfully been used by companies to detect significant and nonsignificant experimental results early, even with small sample sizes data. With XPro, researcher have been able to introduce new products earlier, while minimizing the chance of costly recalls of problematic drugs. XPro¹s controlled procedures can also help avoid erroneous conclusions that can cost companies billions of dollars and create legal problems.

And now, the easy-to-use graphics feature adds yet another powerful dimension to the program. Data analysts can use this simple one-step plotting utility to quickly view and assess data patterns --- all in the midst of performing various analyses.

XPro Statistical Procedures

One and Two-Sample Inference

• Testing and intervals for variance differences and ratios
• Testing and intervals for means
• Equal Variances
• Unequal Variances

One-Way ANOVA

• Testing the equality of means under:
  • Equal Variances
  • Unequal Variances
• Exact likelihood ratio test for testing the equality of variances
• Planned and post hoc multiple comparisons

Two-Way ANOVA

• Testing the equality of means under:
  • Homoscedasticity
  • Heteroscedasticity
• Unbalanced models
• Nested designs

Inference in Mixed Models

• Tests and confidence intervals for variance components:
  • F-tests and Generalized F-tests
  • Khuri-Littel and Weerahandi tests
  • Tukey-Williams tests
  • Generalized Wald intervals
• Comparing variance components from two balanced models, Zhou-Mathew test
• Unbalanced models

Repeated Measures & Growth Curves

• Mixed models without growth patterns
• Mixed models with growth patterns
• Multivariate models

Regression

• Weighted least squares regression
• Power, exponential, and polynomial regressions
• Comparing two regressions under:
  • Homoscedasticity
  • Heteroscedasticity

Multivariate Analysis

• One and two sample models
• MANOVA

Charts

• Combo Charts: Line chart, Point chart, Bar chart, 3D bar chart, Gantt chart
• X-Y Type Charts
• Distribution Charts: histograms, SD bar charts, SE bar charts

Utilities

• Quantiles and Probabilities of widely used distributions
• Random number generation
• Summary statistics

System Requirements

• IBM PC or compatible systems
• Windows 3.1, Windows 95, or Windows NT (for Windows versions)
• 2MB disk space and 512K MB RAM
• Math coprocessor (optional, but recommended)

FAQs

What's so special about XPro?

XPro computes exact p-values for testing hypotheses and computes confidence intervals based on exact probability statements. In particular, it supports exact inference in various linear models. It has been proven to be able to detect significant and nonsignificant experimental results early, even with small sample sizes.

What is "exact statistics"?

Exact statistics is a branch of statistics that was developed to provide more accurate results pertaining to statistical testing and interval estimation by eliminating some of the unreasonable assumptions that traditional statistical methods use. The topic of exact statistics is described in detail in "Exact Statistical Methods for Data Analysis" by Dr. S. Weerahandi. Exact Statistical methods has also been taught at numerous ASA courses and other forums.

What is wrong with classical statistical methods?

Traditional tests and confidence intervals that are usually included in all-purpose statistical software are based on unreasonable assumptions or are approximate methods. Therefore, these outdated approximate methods can introduce unnecessary risks into decisions. For example, classic F-tests in linear models are based on the assumption of equal error variances --- an assumption made for simplicity and mathematical tractability, rather than accuracy of results.

While there is nothing wrong with these procedures when the assumptions are reasonable and/or when the sample size is large, these requirements are often not met in real world situations. Application of a statistical procedure when its performance is poor can lead to very serious repercussions, especially in biomedical and other types of experiments.

Can you demonstrate advantages of exact parametric statistical methods?

Yes, an example of the superior power of exact parametric methods and results of a simulation study on size performance of exact methods compared to asymptotic methods is provided in the XPro examples page.

Other software products claim to employ exact statistic. How is XPro different from these programs?

XPro is the world's only software package specializing in exact parametric methods such as those in ANOVA, Mixed Models, Repeated Measures, Growth Curves, MANOVA, and Regression. XPro procedures are complimentary to such program as StatXact which specialize in exact non-parametric methods. Most programs provide exact parametric methods under assumptions such as the assumption of equal variances in ANOVA. XPro provides procedures based on milder assumptions.

To make this possible XPro performs high dimensional numerical integrations and solves highly nonlinear equations. XPro makes use of efficient algorithms tailor made for exact inferences in linear models and provides an easy-to-use interface that facilitates all necessary analyses.

Who can benefit from XPro?

Commercial, academic, and government statisticians and statisticians who need to perform the parametric statistical inference in applications --- such as Regression, ANOVA Fixed/Mixed Effects Models, Repeated Measures Models, and Growth Curve Models --- can take advantage of XPro's powerful tools.

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