IBM SPSS Exact Tests

Note: Before using this information and the product it supports, read the general information under Notices on page 213. This edition applies to IBM® SPSS® Exact Tests 21 and to all subsequent releases and modifications until otherwise indicated in new editions. Microsoft product screenshots reproduced with permission from Microsoft Corporation. Preface Exact Tests™ is a statistical package for analyzing continuous or categorical data by exact methods. The goal in Exact Tests is to enable you to make reliable inferences when your data are small, sparse, heavily tied, or unbalanced and the validity of the corresponding large sample theory is in doubt. This is achieved by computing exact p values for a very wide class of hypothesis tests, including one-, two-, and K-sample tests, tests for unordered and ordered categorical data, and tests for measures of association. The statistical methodology underlying these exact tests is well established in the statistical literature and may be regarded as a natural generalization of Fisher's exact test for the single contingency table. It is fully explained in this user manual. The real challenge has been to make this methodology operational through software development. Historically, this has been a difficult task because the computational demands imposed by the exact methods are rather severe. We and our colleagues at the Harvard School of Public Health have worked on these computational problems for over a decade and have developed exact and Monte Carlo algorithms to solve them. These algorithms have now been implemented in Exact Tests. For small data sets, the algorithms ensure quick computation of exact p values. If a data set is too large for the exact algorithms, Monte Carlo algorithms are substituted in their place in order to estimate the exact p values to any desired level of accuracy. These numerical algorithms are fully integrated into the IBM® SPSS® Statistics system. Simple selections in the Nonparametric Tests and Crosstabs dialog boxes allow you to obtain exact and Monte Carlo results quickly and easily. Acknowledgments Exact Tests is the result of a collaboration between Cytel Software Corporation and SPSS Inc. The exact algorithms were developed by Cytel. Integrating the exact engines into the user interface and documenting the statistical methods in a comprehensive user manual were tasks shared by both organizations. We would like to thank our fellow developers , 2 2 × iv We owe a special debt to Professor Marvin Zelen for creating an …