STATA May 1995 TECHNICAL STB-25 BULLETIN A publication to promote communication among Stata users Editor Associate Editors Sean Becketti Francis X. Diebold, University of Pennsylvania Stata Technical Bulletin Joanne M. Garrett, University of North Carolina 8 Wakeman Road Marcello Pagano, Harvard School of Public Health South Salem, New York 10590 James L. Powell, UC Berkeley and Princeton University 914-533-2278 J. Patrick Royston, Royal Postgraduate Medical School 914-533-2902 FAX stb@stata.com EMAIL Subscriptions are available from StataCorporation, email stata@stata.com, telephone 979-696-4600 or 800-STATAPC, fax 979-696-4601. Current subscription prices are posted at www.stata.com/bookstore/stb.html. Previous Issues are available individually from StataCorp. See www.stata.com/bookstore/stbj.html for details. Submissions to the STB, including submissions to the supporting files (programs, datasets, and help files), are on a nonexclusive, free-use basis. In particular, the author grants to StataCorp the nonexclusive right to copyright and distribute the material in accordance with the Copyright Statement below. The author also grants to StataCorp the right to freely use the ideas, including communication of the ideas to other parties, even if the material is never published in the STB. Submissions should be addressed to the Editor. Submission guidelines can be obtained from either the editor or StataCorp. Copyright Statement. The Stata Technical Bulletin (STB) and the contents of the supporting files (programs, datasets, and help files) are copyright c by StataCorp. The contents of the supporting files (programs, datasets, and help files), may be copied or reproduced by any means whatsoever, in whole or in part, as long as any copy or reproduction includes attribution to both (1) the author and (2) the STB. The insertions appearing in the STB may be copied or reproduced as printed copies, in whole or in part, as long as any copy or reproduction includes attribution to both (1) the author and (2) the STB. Written permission must be obtained from Stata Corporation if you wish to make electronic copies of the insertions. Users of any of the software, ideas, data, or other materials published in the STB or the supporting files understand that such use is made without warranty of any kind, either by the STB, the author, or Stata Corporation. In particular, there is no warranty of fitness of purpose or merchantability, nor for special, incidental, or consequential damages such as loss of profits. The purpose of the STB is to promote free communication among Stata users. The Stata Technical Bulletin (ISSN 1097-8879) is published six times per year by Stata Corporation. Stata is a registered trademark of Stata Corporation. Contents of this issue page an54. STB-19–STB-24 available in bound format 2 dm28. Calculate nice numbers for labeling or drawing grid lines 2 dm29. Create T E X tables from data 3 dm30. Comparing observations within a data file 7 sg26.3. Fractional polynomial utilities 9 sg32.1. Variance inflation factors and variance-decomposition proportions: Correction 13 sg35. Robust tests for the equality of variances 13 sg36. Tabulating the counts of multiple categorical variables 15 sg37. Orthogonal polynomials 17 sg38. Generating quantiles 19 sg39. Independent percentages in tables 20 snp8. Robust scatterplot smoothing: enhancements to Stata’s 23 sts10. Prais–Winsten regression 26 zz5. Cumulative index for STB-19–STB-24 29