A USER S GUIDE TO WesVarPC

Transcription

1 A USER S GUIDE TO WesVarPC Westat Copyright 1997 Version 2.1 Westat, Inc Research Boulevard Rockville, MD February 1997

2 A User s Guide to WesVarPC Authors: Brick, J.M., Broene, P., James, P., and Severynse, J. Published by: Westat, Inc., Rockville, Maryland, USA Warranty disclaimer: This software and its associated documentation is provided without warranty of any kind, either expressed or implied. Copyright notice: Copyright 1997 Westat, Inc., 1650 Research Boulevard, Rockville, MD, USA. Resale of this software is prohibited. This software may be duplicated for noncommercial purposes provided that a complete paper copy or the complete electronic version of the associated Westat documentation, including this notice, is distributed with each duplicate copy. Duplication of this software or its documentation for commercial purposes requires the written consent of Westat, Inc. Registration of use: Users of this software are requested to register free of charge with Westat, Inc. in order to receive updates and information about future releases. To register, send an to WesVar@Westat.com. Registered trademarks: Adobe is a registered trademark of Adobe Systems, Inc. Microsoft, Microsoft Word, MS, MS-DOS, Excel, Windows 3.1, Windows 95, Windows Program Manager, and Windows NT are registered trademarks of Microsoft Corporation. SAS and PC-SAS are registered trademarks of SAS Institute Inc. dbase is a registered trademark of Borland International, Inc. WordPerfect is a registered trademark of WordPerfect Corporation. SPSS is a registered trademark of SPSS, Inc.

3 ACKNOWLEDGMENTS Our thanks to the many PROC WESVAR and WesVarPC testers and users and other survey researchers who gave us comments and suggestions in the development of this program. Many of the enhancements in this version are based on your feedback. We welcome your continued advice. One of our goals was to create a user-friendly environment that makes it easier to specify requests--and to modify and resubmit requests. We also tried to take advantage of the Windows environment to make WesVarPC more powerful, easier to use, and as intuitive as possible by taking advantage of Window s point & click interface. The programmers who developed WesVarPC have spent a great deal of time in making it user-friendly. We believe their enthusiasm and skill have been translated into a valuable tool for the survey community. The WesVarPC Development Team The persons who were formally responsible for the development of WesVarPC are listed below: Design: Programming: Documentation: Mike Brick Wen-Chau Haung Mike Brick David Judkins Warren Mason Pam Broene Leyla Mohadjer Debby Vivari Penny James David Morganstein Keith Rust Angelia Murphy Jacqueline Severynse Nancy Speicher In addition to the development team many members of Westat have played important roles in documenting and testing earlier versions of this software. David Becher, Shelley Brock, Tom Brundage, Ismael Flores-Cervantes, Tom Mule, Mary Gessley Nixon, and Julie O Connell were key testers of the software. We thank these and other members of the staff who have helped make this product possible.

4 Welcome to WesVarPC WesVarPC is a software package developed at Westat, Inc. that computes estimates and replicate variance estimates from survey data collected using complex sampling and estimation procedures. WesVarPC reads a variety of input files and creates a WesVarPC file. After creating a WesVarPC file, sampling errors can be estimated for different types of survey statistics. This software supports a wide range of complex sample designs, including multistage, stratified, and unequal probability samples. The replicate variance estimation method can deal with many types of estimation schemes, such as poststratification or ratio estimation. Also, WesVarPC computes estimates of variances for medians, percentiles and complex functions of estimates including ratios, differences of ratios and log-odds ratios. Tests of hypotheses for tables can be performed using chi-square statistics that have been adjusted for the complex survey design. WesVarPC computes parameter estimates for linear and logistic regression models. Along with providing a test for the overall fit of the regression model, WesVarPC can perform tests for the significance of linear combinations of variables included in the model. WesVarPC is the only well-documented PC-based program available today that uses the replication method for variance estimation. It is also the only Windows-based system allowing easy access to variance estimation for survey researchers needing to analyze data from complex surveys. Where to Start: A Road Map to this Book If you... Start with... Want an overview of WesVarPC Chapter 1 Are familiar with replicate variances, but have not used Westat s software Have used earlier versions of WesVarPC, PROC WESVAR, PROC WESREG, or PROC WESLOG, and you want to try the new version Are a data processing professional using WesVarPC for someone else Chapter 2 Chapter 3 Chapter 3, technical appendices

5 February 1997 Table of Contents iii TABLE OF CONTENTS Chapter Page 1 An Overview of WesVarPC... 1 Introducing WesVarPC... 1 The Benefits of WesVarPC... 2 Some Basic Information... 3 Who Should Use WesVarPC... 3 What You Need to Get Started... 4 What You Need to Know... 4 How WesVarPC Differs From PROC WESVAR, WESREG, and WESLOG... 5 Naming Conventions Used in This Manual... 6 Helpful Notes Before Using WesVarPC... 7 New Features in Version Prep Menu... 8 Format Menu... 8 Tables Menu... 8 Regression Menu... 9 Browse Menu... 9 New Features in Version Regression Menu... 9 Prep Menu Tables Menu Browse Menu Documentation Version 2.1 Release Notes Version 2.0 Release Notes Suggestions, Problems, or Comments Getting Started Preface Obtaining WesVarPC Step 1: Downloading WesVarPC Installation Files Step 2: Installing WesVarPC Step 3: Installing the Adobe Acrobat Reader... 15

6 iv Table of Contents February 1997 TABLE OF CONTENTS (Continued) Chapter Page 2 Running WesVarPC Test Data WesVarPC: Process Flows WesVarPC Help Examples Using WesVarPC Example Importing the SAS File (Prep) Formatting the File (Format) Creating the Tables Request (Tables) Example Example Example Prep: Create a WesVarPC Data File Import a Data File Import SAS and SAS Transport Files Import a SPSS for Windows or dbase File Importing an ASCII File Modify a WesVarPC Data File Create Replicate Weights Poststratification Attach Factors Subpop WesVarPC Data File Extract WesVarPC Data File Preferences Format: Formatting Labels and Recoding Variables Labels Recodes... 88

7 February 1997 Table of Contents v TABLE OF CONTENTS (Continued) Chapter Page 6 Tables: Computing Estimates and Their Variances in Tables New and Open Analysis Button Compute Button Means Medians and Other Quantile Estimates Tables Button Tables Options Function Statistics Input Button Output Button Subset Button Table Summary Run Button View Button Save Button Batch Wvq Create Table Output Regression: Defining Models and Testing Hypotheses New and Open New and Modify Buttons Clone Button Delete Button Input Button Output Button Run Button View Button Save Button Batch

8 vi Table of Contents February 1997 TABLE OF CONTENTS (Continued) Chapter Page 8 Browse: Looking at Output Files Output Listings WesVarPC Data File About WesVarPC References List of Appendices Technical Appendix Page A Introduction to Replication Methods for WesVarPC B Estimates From Tables Menu C Models in Regression Menu D Special Output Feature in Tables E Manually Creating.WVQ Files Figure List of Figures Page 2-1 WesVarPC Icon on Desktop WesVarPC Group Box Warranty Disclaimer Introducing WesVarPC WesVarPC Main Menu Process Flow Map WesVarPC Help Contents Import SAS Data File Creating Weights for WesVarPC Data File Select Variables for Recoding Recode (Discrete) Create Recodes Label Variables Table Request Select Analysis Variables Compute Statistic Define Tables Tables... 35

9 February 1997 Table of Contents vii TABLE OF CONTENTS (Continued) List of Figures (Continued) Figure Page 3-12 Table Request Table Cell Definition Create Function Statistic Recode (Discrete) Cell Definition Create Function Statistic Tables Table Request Regression Request Define Linear Model Create Hypothesis Testing Define Linear Model Regression Request WesVarPC Main Menu Import SAS Data File Import SAS Data File Import ASCII Data File ASCII Data File Layout Import ASCII Data File Modify WesVarPC Data File Creating Weights for WesVarPC Data File Poststratification Attach Factors for Data File Create Subpopulation Select Variables to be Extracted Preferences Selection Menu General Preferences Table Preferences Regression Preferences Format Selection Menu Label Variables Create Recodes Recode (Discrete) Select Variables Recode (Discrete) Recode (Continuous) Recode (Continuous) Create Recodes TABLE OF CONTENTS (Continued)

10 viii Table of Contents February 1997 List of Figures (Continued) Figure Page 6-1 Tables Selection Menu Table Request Select Analysis Variables Compute Statistic Tables Define Table Cell Definition Create Function Statistic Table Output Control Select Subset Criteria Table Request Run Request(s) Create Request File Regression Selection Menu Regression Request Define Logistic Model Select By Variables Create Hypothesis Testing Independent Variables Initial Values Select Success Value for Dependent Variable Regression Request Regression Output Control Browse Selection Menu Output Listings Browse List of Exhibits Exhibit Page 3-1 Output Listing for TABLE1.WVQ Output Listing for TABLE2.WVQ Output Listing for TABLE3.WVQ Output for MODEL1.WVR... 59

11 AN OVERVIEW OF WesVarPC CHAPTER 1 This chapter introduces WesVarPC and discusses issues pertaining to WesVarPC that apply throughout the software. Examples of such issues are how to choose variables and how to create equations. Chapter 2 includes installation instructions. Chapter 3 contains detailed examples for the user to see exactly how the software works. Chapters 4 through 8 discuss each of the five main menu items; Prep, Format, Tables, Regression, and Browse, respectively. These chapters contain the in-depth information the user needs to specify the request. The appropriate screens are displayed as well. In addition, there are five technical appendices for the user who needs to learn about replication methods for WesVarPC and estimates from the Tables and Regression menus. Appendix A discusses some basic ideas associated with the replication approach. Appendix B explains the ways in which the estimates and standard errors are produced from the Tables menu. Appendix C describes the methodology for linear and logistic regression models. Appendix D describes methods of exporting the output of tables directly into spreadsheets for presentation purposes. Appendix E explains methods that can be used to produce a table request without using the WesVarPC interface. Introducing WesVarPC WesVarPC is a software package that computes estimates and replicate variance estimates for data collected using complex sampling and estimation procedures. This flexible software supports a wide range of complex sample designs, including multistage, stratified, and unequal probability samples. The replicate variance estimates can also reflect many types of estimation schemes, such as poststratification or ratio estimation. With WesVarPC, it is relatively simple to compute variance estimates for complex functions of estimates, including ratios, differences of ratios, and log-odds ratios. WesVarPC calculates sampling errors, variances, and confidence intervals for the survey estimates you specify, as well as chi-square tests of independence for two-way tables of weighted frequencies.

12 2 Chapter 1 - An Overview of WesVarPC February 1997 WesVarPC also computes estimated coefficients for linear and logistic regression models and will test for the significance of a subset of linear combinations of variables you specify. WesVarPC gives you four replication options for estimating sampling errors: Balanced repeated replication (BRR); Two jackknife methods (JK1 and JK2); and Fay s method (FAY). For a description of these four replication methods, see Appendix A. Replication offers a number of important benefits: Provides a relatively simple way of estimating variances without doing analytic derivations; Allows you to estimate sampling errors for a wide variety of types of estimates (ratio, difference of proportions, log-odds ratio, regression coefficients, etc.); Appropriately reflects the impact of the nonresponse adjustments, poststratification, and other types of weight adjustments in the variance estimates--if you include these adjustments in your replicate weights; and Produces variance estimates having low relative bias for nonlinear statistics based on relatively small sample sizes. The Benefits of WesVarPC With WesVarPC, you can: Import PC-SAS for DOS, SAS Transport, SPSS for Windows, DBF or ASCII data files; Create replicate weights for standard sample designs if you do not already have them; Recode, relabel, and reformat variables; Calculate variances for analysis variables including complex transformations of the original survey variables and regression parameters;

13 February 1997 Chapter 1 - An Overview of WesVarPC 3 Browse output files before you print them; and Control the format of output files for direct input to a spreadsheet or other software for customizing the output or doing additional computations. You can compute tables of survey estimates with their standard errors. You can also define linear or logistic regression models, estimate the model parameters and test the fit of the models. WesVarPC offers a number of important benefits to users: Speed; Convenience; Independence from specialized data processing support; A procedure to develop replicate weights that are retained for future analysis; The creation of a data file that can be used to make multiple requests; A method of examining the output without printing; Output files that can be easily used with other software; and Table or regression requests that can be easily modified and resubmitted. Some Basic Information Who Should Use WesVarPC WesVarPC is designed for survey researchers, social scientists, and others who want to compute sampling errors for survey data collected using a complex design and: Have survey data in data files; Have some knowledge of Windows 3.1 or Windows 95; and

14 4 Chapter 1 - An Overview of WesVarPC February 1997 Know about replication methods or are willing to spend a little time learning about it (see Appendix A). What You Need to Get Started A 386 or more powerful personal computer with a math co-processor (4 megs of RAM recommended) and at least 4 megs of hard disk space (just for file storage). If you do not have a math co-processor, send an to Wesvar@Westat.com requesting a version for machines without the co-processor; Windows 3.1 or Windows 95 (both versions are available), with a mouse; and WesVarPC installed (see the installation instructions in Chapter 2). What You Need to Know Before you proceed, you should be able to answer yes to the following questions: Do you understand the meaning of replicate variance estimation? Do you know how replicate weights can be used to compute variance estimates? (If in doubt, refer to Appendix A.) Do you know the contents of your input data file? Does it include replicate weights? If not, do you know the design parameters (primary sampling units and strata) needed to create replicate weights using WesVarPC? (Refer to Appendix A.) Do you know the kinds of estimates for which you want to estimate variances? Do you understand how you can form these estimates using WesVarPC? (Refer to Appendix B.) Do you know what type of regression model you want to specify and what variables you want to include in the model? (Refer to Appendix C.) The flexibility of the software is also a potential disadvantage. For example, if you are not familiar with variance estimation for complex samples, you may produce estimates inappropriately. WesVarPC does not provide a mechanism to reflect nonresponse and other postsurvey adjustments, except poststratification adjustments, in the replicate weights that it prepares.

15 February 1997 Chapter 1 - An Overview of WesVarPC 5 To reflect these types of adjustments in your estimates, you must create replicate weights before using WesVarPC. (See Appendix A for more information.) To create replicate weights, you will need the details of the sample design such as PSU and strata indicators. If you need to know more, see Appendix A and study the documentation to find out more about the design of your survey and the contents of the data file. Many designs can be accommodated under the replication procedures supported by WesVarPC, but a sampling statistician with expertise in replication methods may be required to take full advantage of replication methods in defining the appropriate procedures in your application. How WesVarPC Differs From PROC WESVAR, WESREG, and WESLOG PROC WESVAR, WESREG, and WESLOG are mainframe software applications that Westat developed in the 1980s to compute sampling errors using replication methods. WesVarPC is a new, improved Windows-based version. Some differences are: WesVarPC (new) Stand-alone PC program that is independent of SAS Procedure that can import a variety of data files Replicate weights for standard sample designs can be created or previously created ones can be used Multidimensional tables can be analyzed Two methods of handling missing analysis variables Some formatting and recoding capability supported in the procedure PROC WESVAR, WESREG, and WESLOG (old) User-written procedure that works only within SAS on a mainframe SAS data files are needed to use the procedures Replicate weights must already be in the data file Only two-dimensional tables supported One method of handling missing variables All formats and recodes must be done in SAS before using procedure

16 6 Chapter 1 - An Overview of WesVarPC February 1997 WesVarPC (new) (continued) User-friendly requests are made by clicking on variable names and using a built-in calculator to define computed statistics and table or regression requests; requests can be saved for later, easy modification. Advanced users can create batch request files to produce large numbers of tables. Can specify hypothesis tests for both linear and logistic regression models Categorical variables are automatically coded as class variables for use in defining regression models Can run regression model requests for each level of a variable Linear and logistic models may include interaction terms Can compute the median or specified quantiles of variables along with their standard errors PROC WESVAR, WESREG, and WESLOG (old) (continued) Requests are prepared in a SAS-like language Hypothesis testing available only for linear regression models Categorical variables must be recoded in SAS as class variables before using the procedure Must recode a variable in SAS and run separate regression requests for each level of the variable Regression models only allow main effects No medians or quantiles could be computed Naming Conventions Used in This Manual In the documentation that follows, references to screens are italicized. References to menus, menu items and buttons appear as they do on the screen, with the hot-key underlined. (A hotkey is the keyboard short-cut that can be typed rather than clicking on the screen.) Variable names are capitalized in the text. Naming conventions have been adopted for the files created and used in WesVarPC. In general, you can specify up to eight characters for the prefix name. However, WesVarPC assigns the following names for the file extensions:

17 February 1997 Chapter 1 - An Overview of WesVarPC 7 Type of File Extension Data var Table Request wvq Regression Request wvr Output Listing lst Output Extract: ASCII Data (Tables only) dat Binary Data (Tables only) bin SAS Program (Tables only) sax Export Files: Metafile (Tables only) mtf Raw Data File (Tables only) tbn Output Outest (Tables only) est Output Debug (Regression only) bug Output Printrep (Regression only) rep Helpful Notes Before Using WesVarPC For WesVarPC, there are certain conventions that are valid throughout the program: WesVarPC is not case sensitive, i.e., it will not distinguish between the same variable name on the basis of capital and small letters. For example, AGE, age and Age are treated as one and the same variable. The action verbs on the right of any screen (e.g. Create, Select, Run, View) are referred to as buttons. To select or deselect a variable, double click on the variable. The double click is like a toggle or on/off switch. You can also highlight the variable by clicking on it once, then move it using the arrow keys provided on most screens. Users can move across boxes on a screen by using the tab key or by using the mouse and clicking in the box desired. To create a statistic that is a function of weighted totals (e.g. in the Compute or Function section of Tables), the user must specify the statistic to be computed (or dependent variable) and also specify the function of other variables used to create the new variable. The same procedure is used to define regression equations. Buttons that include a trailing ellipsis or dots such as... after a word indicate you may go to that screen to perform additional tasks by clicking on the button.

18 8 Chapter 1 - An Overview of WesVarPC February 1997 New Features in Version 2.1 New A number of important substantive changes have been made in Version 2.1, and these are highlighted below. Because of the impact of these changes on many aspects of the program and its operation, this manual has been revised and each of the changes is described in more detail in the appropriate chapters of the manual. Version 2.1 can be run using either a Windows bit processor or Windows 3.1. Both versions can be downloaded from the URL. Prep Menu A new method of setting defaults for options in a Preferences file is given. The factor statement can be used with up to 256 replicate weights. The layout for importing an ASCII file can be imported from an external file. Input files with negative, zero, or missing weights can be imported. It is possible to import SPSS 7.5 and more information on importing and exporting SAS transport files is in the manual. A method of creating replicate weights that are raked is described. Format Menu A method of creating recodes of continuous variables is included. Tables Menu A method for computing medians and other quantiles has been added. The ability to choose a FOR variable that uses percents, row percents or column percents in the definition of a function statistic is included.

19 February 1997 Chapter 1 - An Overview of WesVarPC 9 A completely new method for creating a table request without using the graphical interface has been developed. A new output that gives the t-value for the test that the estimate is zero and the probability is provided. The output to the Excel macro has been updated and substantially revised. Regression Menu Three way interactions can now be included in models. The number of spaces available to specify a model is increased to 256. The number of initial values for parameters that can be specified in logistic regression is increased to 45. Transformations of dependent variables in linear regression is supported. Browse Menu A new method of summarizing the contents of the WesVarPC data file is added. New Features in Version 2.0 Some of the important new features in Version 2.0 are highlighted below. There are many additional new features described in the later chapters of the manual. Regression Menu An entirely new menu has been added to support linear and logistic regression analysis. A chapter in this manual and an appendix documenting regression methods are also provided.

20 10 Chapter 1 - An Overview of WesVarPC February 1997 Prep Menu Import will now support importing additional data file formats: SPSS for Windows, SAS Transport, and DBF files. It is no longer necessary to specify the record length (LRECL) when importing ASCII files. An output of the results of Poststratification is now provided to enable users to view the poststratification adjustments. A new Extract Variables item enables the user to output the contents of a WesVarPC file, including the replicate weights, to a user defined output file. A new Subfile item enables users to make a subset WesVarPC file that is restricted to records with specific characteristics. The constants in the Factor statement can now be read from an external file in addition to being directly entered in the menu item. Tables Menu The Complete option can now be turned OFF to allow analysis variables with missing values to be handled independently of other analysis variables in the same Table Request. (When the Complete option is ON (in version 1.1 and earlier this was the only mode), any observation with any analysis variable or compute statistic with missing values is dropped from all the computations in the Table Request.) The Subset option allows users to specify that all processing should be restricted to observations in a particular subdomain. List output can be saved in a specially formatted file for camera-ready formatting in Excel using a macro included with WesVarPC. Browse Menu The Print option has been enhanced so that the output format examines the print driver options and automatically makes the printed output conform to the paper size.

21 February 1997 Chapter 1 - An Overview of WesVarPC 11 An option has been added to output files so that they can be directly input into Excel or other spreadsheet software. An Excel spreadsheet with a macro to read the input WesVarPC output file is included. Documentation Appendices D and E describe how advanced users can export tables directly into spreadsheets for presentation purposes and how users can prepare batch requests. Version 2.1 Release Notes Many of the features of WesVarPC have been upgraded in this new version. In addition, new features have been added. We hope to continue to make modifications to the program based on feedback from users. Version 2.0 Release Notes This version of WesVarPC completely replaces and enhances the capabilities of earlier versions of WesVarPC, WESVAR, WESREG and WESLOG. In the future we plan to examine other statistical procedures and determine if these procedures should be added to the current system. In particular, we are studying methods of quantile estimation. We also plan to examine other ways to make the software more extensive and user-friendly, such as allowing the user to set their own defaults for options. Suggestions, Problems, or Comments Please help us improve WesVarPC. If you have any suggestions, problems, or other comments, send an message to: WESVAR@Westat.com.

22 12 Chapter 1 - An Overview of WesVarPC February 1997 A listserver for discussion regarding WesVarPC and other replication variance estimation issues has been established. To subscribe to the listserver, send an message to: listserv@listserv.westat.com. In the body of the message, write the following message: subscribe WESVAR-L <your name>. Once you have subscribed, messages to be distributed should be sent to WESVAR-L@listserv.westat.com. Note All updates and new versions of the software will be announced on the listserver. This is an excellent way to ensure you have the most current version of the software. When notifying us of any problems you have with the software, please be sure to include in your message what version of the software you are using. This information may be obtained by clicking on Browse in the main menu and then clicking on the submenu About WesVarPC.