[U] User's Guide - Stata

1 Stata user S GUIDERELEASE 17 A Stata Press PublicationStataCorp LLCC ollege Station, Texas Copyrightc 1985 2021 StataCorp LLCAll rights reservedVersion 17 Published by Stata Press, 4905 Lakeway Drive, College Station, Texas 77845 Typeset in TEXISBN-10: 1-59718-353-9 ISBN-13: 978-1-59718-353-6 This manual is protected by copyright. All rights are reserved. No part of this manual may be reproduced, storedin a retrieval system, or transcribed, in any form or by any means electronic, mechanical, photocopy, recording, orotherwise without the prior written permission of StataCorp LLC unless permitted subject to the terms and conditionsof a license granted to you by StataCorp LLC to use the software and documentation. No license, express or implied,by estoppel or otherwise, to any intellectual property rights is granted by this provides this manual as is without warranty of any kind, either expressed or implied, including, butnot limited to, the implied warranties of merchantability and fitness for a particular purpose.

2 StataCorp may makeimprovements and/or changes in the product(s) and the program(s) described in this manual at any time and software described in this manual is furnished under a license agreement or nondisclosure agreement. The softwaremay be copied only in accordance with the terms of the agreement. It is against the law to copy the software ontoDVD, CD, disk, diskette, tape, or any other medium for any purpose other than backup or archival automobile dataset appearing on the accompanying media is Copyrightc 1979 by Consumers Union of ,Inc., Yonkers, NY 10703-1057 and is reproduced by permission from CONSUMER REPORTS, April ,, Stata Press, Mata,, and NetCourse are registered trademarks of StataCorp and Stata Press are registered trademarks with the World Intellectual Property Organization of the United is a trademark of StataCorp brand and product names are registered trademarks or trademarks of their respective copyright information about the software, typehelp copyrightwithin suggested citation for this software isStataCorp.

3 : Release 17. Statistical Software. College Station, TX: StataCorp basics1 Read this it will help ..22A brief description of Stata ..93 Resources for learning and using Stata ..134 Stata s help and search facilities ..245 Editions of Stata ..316 Managing memory ..347 more conditions ..368 Error messages and return codes ..379 The Break key ..4010 Keyboard use ..42 Elements of Stata11 Language syntax ..4912 Data ..8413 Functions and expressions ..12314 Matrix expressions ..14415 Saving and printing output log files ..15916Do-files ..16517 Ado-files ..17818 Programming Stata ..18319 Immediate commands ..23520 Estimation and postestimation commands ..23921 Creating reports ..301 Advice22 Entering and importing data ..30523 Combining datasets ..314iii Contents24 Working with strings.

4 31625 Working with dates and times ..32026 Working with categorical data and factor variables ..32927 Overview of Stata estimation commands ..34728 Commands everyone should know ..38129 Using the Internet to keep up to date ..383 Glossary ..390 Subject and author index ..395 Stata basics1 Read this it will help ..22A brief description of Stata ..93 Resources for learning and using Stata ..134 Stata s help and search facilities ..245 Editions of Stata ..316 Managing memory ..347 more conditions ..368 Error messages and return codes ..379 The Break key ..4010 Keyboard use ..4211 Read this it will Started with Stata .. user s Guide and the Reference manuals .. manuals .. example .. datasets .. example .. index .. subject table of contents .. s new ..82[ U ] 1 Read this it will help 3 The Stata Documentation consists of the following manuals.

5 [GSM]Getting Started with Stata for Mac[GSU]Getting Started with Stata for Unix[GSW]Getting Started with Stata for Windows[U] Stata user s Guide [R] Stata Base Reference Manual[BAYES] Stata Bayesian Analysis Reference Manual[CM] Stata Choice Models Reference Manual[D] Stata Data Management Reference Manual[DSGE] Stata Dynamic Stochastic General Equilibrium Models Reference Manual[ERM] Stata Extended Regression Models Reference Manual[FMM] Stata Finite Mixture Models Reference Manual[FN] Stata Functions Reference Manual[G] Stata Graphics Reference Manual[IRT] Stata Item Response Theory Reference Manual[LASSO] Stata Lasso Reference Manual[XT] Stata Longitudinal-Data/Panel-Data Reference Manual[META] Stata Meta-Analysis Reference Manual[ME] Stata Multilevel Mixed-Effects Reference Manual[MI] Stata Multiple-Imputation Reference Manual[MV] Stata Multivariate Statistics Reference Manual[PSS] Stata Power, Precision, and Sample-Size Reference Manual[P] Stata Programming Reference Manual[RPT] Stata Reporting Reference Manual[SP] Stata Spatial Autoregressive Models Reference Manual[SEM] Stata Structural Equation Modeling Reference Manual[SVY] Stata Survey Data Reference Manual[ST] Stata Survival Analysis Reference Manual[TABLES] Stata Customizable Tables and Collected Results Reference Manual[TS] Stata Time-Series Reference Manual[TE] Stata Treatment-Effects Reference Manual.

6 Potential Outcomes/Counterfactual Outcomes[ I ] Stata Index[M]Mata Reference ManualIn addition, installation instructions may be found in theInstallation [ U ] 1 Read this it will Getting Started with StataThere are threeGetting Startedmanuals:[GSM]Getting Started with Stata for Mac[GSU]Getting Started with Stata for Unix[GSW]Getting Started with Stata for Windows1. Learn how to use Stata read theGetting Started(GSM,GSU, orGSW) Now turn to the other manuals; see[U] The user s Guide and the Reference The user s Guide and the Reference manualsTheUser s Guideis divided into three sections: Stata basics,Elements of Stata , andAdvice. Thetable of contents lists the chapters within each of these sections. Click on the chapter titles to see thedetailed contents of each full of a lot of useful information about Stata ; we recommend that you read it.

7 Ifyou only have time, however, to read one or two chapters, then read[U] 11 Language syntaxand[U] 12 other manuals are theReferencemanuals. The StataReferencemanuals are each arrangedlike an encyclopedia alphabetically. Look at theBase Reference Manual. Look under the name ofa command. If you do not find the command, look in the subject index in [I] Stata Index. A fewcommands are so closely related that they are documented together, such asranksumandmedian,which are both documented in [R] all the entries in theBase Reference Manualare Stata commands; some contain technicalinformation, such as [R]Maximize, which details Stata s iterative maximization process, or [R]Errormessages, which provides information on error messages and return an encyclopedia, theReferencemanuals are not designed to be read from cover to you want to know what a command does, complete with all the details, qualifications, andpitfalls, or when a command produces an unexpected result, read its description.

8 Each entry is writtenat the level of the command. The descriptions assume that you have little knowledge of Stata sfeatures when they are explaining simple commands, such as those for using and saving data. Formore complicated commands, they assume that you have a firm grasp of Stata s other a Stata command is not in theBase Reference Manual, you can find it in one of the otherReferencemanuals. The titles of the manuals indicate the types of commands that they contain. TheProgramming Reference Manual, however, contains commands not only for programming Stata butalso for manipulating matrices (not to be confused with the matrix programming language describedin theMata Reference Manual). PDF manualsEvery copy of Stata comes with Stata s may be accessed from within Stata by selectingHelp>PDF more convenient, every help file in Stata links to the equivalent manual entry.

9 If you are readinghelp regress, simply click on(View complete PDF manual entry)below the title of the help fileto go directly to the [R]regressmanual provide some tips for viewing Stata sPDFdocumentation at [ U ] 1 Read this it will help Video examplePDFdocumentation in Example datasetsVarious examples in this manual use what is referred to as the automobile dataset, Wehave created a dataset on the prices, mileages, weights, and other characteristics of 74 automobilesand have saved it in a file (These data originally came from the April 1979 issueofConsumer Reportsand from the United States GovernmentEPAstatistics on fuel consumption;they were compiled and published by Chambers et al. [1983].)In our examples, you will often see us type. use include with Stata . If you want to use it from your own computer rather thanvia the Internet, you can type.

10 Sysuse autoSee [D] can also selectingFile > Example , clicking onExampledatasets installed with Stata , and clicking onusebeside are many other example datasets that ship with Stata or are available over the web. Here isa partial list of the example datasets included with automobile blood-pressure data, long blood-pressure data, wide survival in drug Census data by city temperature and gross domestic gross national product, 1967 life network diagram National Longitudinal Study of Young Women (NLSW), Census population, elevation of Lamont sandstone in an area of 500 historic sea surface time-series life expectancy, 1900 presidential voter dataAll of these datasets may be used or described from theExample more example datasets, including most of the datasets used in the reference manuals, areavailable at the Stata Press website ( ).