Many consultants loved and sought after statistical analysis classes in graduate school. Others avoided them religiously. For both groups, these sites will help you refine and refresh skills.

Introduction to Multilevel Modeling
This site offers a basic understanding of and resources to implement the multilevel modeling approach to statistics. This site would be helpful in explaining the analysis to clients, students and others. It also lists good reference books in the field.

iSixSigma Statistics
The iSixSigma portal site for statistics. This portal offers links on control charts, regression analysis, online statistics textbooks and hypothesis testing, among other resources.

SAS Institute
The SAS Institute is the world's largest privately held software company, and they offer statistical software solutions for business, the public sector and consultants.

SPSS, Inc.
The home page for SPSS software is helpful to the user seeking information on this widely used statistical package. Here you will find information on performance measurement, forecasting, data analysis and data sources.

Stata Statistical Software
Stata is a statistical analysis software package for Windows, Unix and MacIntosh computers. The Stata site offers information about the package as well as articles on the use of their software in various settings. They also offer a bookstore with information on using the program.

Statistical Resources on the Web
This site, offered by the University of Michigan Library, provides links to hundreds of web resources offering statistical information. Topics include agriculture, business, housing, health, and many others.