EQS statistical software provides Structural Equation Modeling and Path Analysis operations without complicated matrix-algebra programming or knowledge. The EQS Structural Equations Program Manual (see References below) provides a good technical overview of Structural Equations and related theory and then relates the elements of that theory to the simple programming language that makes EQS work.

Traditionally, EQS users would write a program and submit it, then view and study the printed output. The Windows and Macintosh retain this approach, of course, but also add such features as an on-screen spreadsheet for data input and/or manipulation, point-and-click analysis, and interactive path-diagrams to assist the building and estimation of models.

The Macintosh or Windows versions of EQS are available only from Multivariate Software, Inc. (see the end of this document for contact information). This software is fully supported by ITS. (ITS also maintains and supports EQS under UNIX for those who have an RCF or an SCF account.)

Launching EQS

To start up EQS, find the EQS (or EQS.PPF) icon, and double-click on it. This brings up the EQS Output window and a Menu bar that allows you to manage your session and get Help if needed. The 'tool bar' displayed near the top is a set of Plot Function Icons, the use of which is explained in the User's Guide for the platform you are using.

The EQS Package

EQS is designed to perform structural modeling, including regression, latent variable, and structural equation models such as Multiple Regression, Multivariate Regression, Path Analysis, Simultaneous Equations, Latent Variable Models, Confirmatory Factor Analysis, Structured Means Analysis, Multiple Population Comparisons, and Monte-Carlo Simulations.

EQS runs in interactive mode on Macintosh and Windows platforms. Most EQS output files are character data, so that they can be sent to virtually any printer. Alternatively, you can save EQS output (and programs, and data) into ASCII files and print them or otherwise use them on other DOS or Macintosh systems.

In terms of command and subcommand syntax, EQS for the Macintosh and EQS for Windows are similar to versions running on other platforms (e.g., UNIX). Most of the differences, of course, relate to differences in the way external files are specified (if and when they are used), a convention which is operating-system-specific.

The EQS programming language is designed to bypass the details of matrix algebra and mathematical calculation, and focus on concepts of data manipulation and Structural Equation modeling. The syntax uses a series of "sections", each of which begins with a slash (/) and a keyword. The standard EQS paragraphs for statistical analysis are /SPECIFICATIONS, which describes the problem to be analyzed, /EQUATIONS, which describes the equations involved in the model under consideration, and /VARIANCES, which specifies the variance for each independent variable in the model. The /END section signals the end of program statements. Several optional sections allow the user to specify tests, constraints, and other special operations.

It is possible to enter data in the same program that is being written to analyze them. This is called "inline" or "instream" data entry, but apparently can only be used when the data are in the form of correlation or covariance matrices. (The appearance of data within a program is introduced by the /MATRIX keyword.) When raw data are used, they are accessed from an external file. The Windows and Macintosh versions of EQS have introduced many new features designed to make the entry and/or manipulation of data, both raw values and matrices, more convenient and straightforward.

The output from EQS jobs contains the original input statements, results of the calculations and plots requested, and any error messages or other notes that might be generated by your program. Output is shown on your screen and can be saved into a file by clicking File>Save As (or File>'Save). If you have not saved information that has been written to the screen and you click File>Quit to exit EQS, the system will ask if you want to save the Output.

The elements of EQS programs are fully documented in the EQS Structural Equations Program Manual (see References at the end of this document), which also contains a fair amount of statistical background text relating to Structural Modeling, including references and suggestions for further reading on the subject.

Input Data

Data may be prepared by analysis for EQS in a number of ways.
• Raw data in rows and columns may be stored in a file in free or column format, and read into EQS through the File>Open method. In order for this method to work, the file name must end with the *.dat extension. For example, raw.txt will not bring up the necessary dialog box for preparing raw data, but raw.dat will. In this method, the Raw Data File Information dialog box allows you to specify delimiters, missing values, lines-per-case, Column Format, and other details. This method results in the creation of a temporary EQS system version of the data which is stored and displayed in the onscreen spreadsheet.
• Remember that EQS can handle only numeric data, not character (alphanumeric).
• Matrix data in the form of covariance coefficients can be specified in a Model (program) file after the /MATRIX specification
• BMDP Save files, Lotus (*.WK*) files and dBase (.DBF) files usually can be read directly into the EQS spreadsheet
• Data may be entered manually into the EQS spreadsheet

Saving and Re-Using EQS System Data [*.ESS] Files

Once raw data have been processed into the EQS program and appear in the onscreen spreadsheet, you can save the data into an EQS system file for future use. That way you will not need to read the raw (or matrix) data again unless the data change somehow (or you lose the .ESS file that you create). To save an EQS system version of your data, click on the data spreadsheet that contains the data you want to save, then click File>Save As (or File>Save if you're sure you know what you're doing), then choose the File Type .ESS, and type in a name (ending in .ESS) for your file.

To re-use .ESS data in future sessions -- in other words, to bring an .ESS file back into the onscreen spreadsheet -- click File>Open, then choose the File Type .ESS, then highlight and open the .ESS file of your choice.

Reading SPSS and BMDP System [*.SAV] Files

As of Release 5.5. EQS for Windows can read SPSS and BMDP system files without intermediate processing. Simply click File>Open, then choose the SPSS (*.SAV) or BMDP (*.SAV) file type, then enter the name of the desired file and open. EQS will open its own data spreadsheet with the data and variable names from the SPSS or BMDP System File.

EQS Programs

The elements of EQS Models (programs) are outlined elsewhere in this document, and of course, are fully explained in the EQS manuals (see References at the end of this document). EQS programs can be stored in files and called into a program window where they can be run, To do this, click File>Open, then choose the File Type .EQS, then highlight the file you'd like to open, then click OK. (Note that the correct drive and path, if any, must also be in place before the file you want will appear in the window.)

If no program file yet exists, you may type a new one directly into an empty program window and then save it (if you wish) for future use. To raise an empty program window, click File>Open, then specify a file name (ending with .eqs) that doesn't yet exist. A dialog box will appear that looks like an error (something about not being able to open whatever.eqs), but when you click OK, you are in a fresh, new window ready to go.

Another alternative for creating EQS Models (programs) is available in the Build EQS menu choice. Here you can point-and-click your instructions (so to speak), and EQS will build a Model (program) for you.

Point-and-Click Analysis

The Macintosh and Windows versions of EQS provide an alternative that makes it unnecessary in many cases to write or run a program at all. Once you have your data in the onscreen spreadsheet (i.e., once you have read your data into EQS), you can click on Analysis and EQS will provide you with an array of analysis choices at the point of your mouse.

Running EQS Programs (Models)

When an EQS Model is visible in the program window it is executed by clicking Build EQS>Run EQS. The output appears on the screen as it runs, and then the output is stored in a file, and the program asks you whether you'd like to inspect that file. Once output files exist (they are saved automatically when a Model [program] runs successfully), they can be printed in the same way as any text file is printed.

Drawing Path Diagrams Interactively

One of the most dramatic innovations of the EQS package for Microcomputers is the ability to draw path diagrams in picture form, and have EQS analyze the Model (and build the program) for you. This process begins by clicking the Diagrammer icon, which is the representation of a three-indicator, one-factor structure. It is at the right of the tool bar. Details and instructions on running the Diagrammer are found in the References and in the online Help in EQS. To see a sample related to the manul7.eqs program (see the section in this document on Sample Programs) click File>Open, then click the file type .EDS, then highlight and open manul7.eds.

The EQS diskettes contain a number of sample files that illustrate the various features of the software. These files normally are installed into your EQS directory along with the software itself. Types of files include:
• EQS System Data [.ESS] (EQS system versions of previously raw data)
• EQS Model Files [*.EQS] (programs that perform analysis)
• Raw Data Files [*.DAT]
• Diagram Files [*.EDS] (saved path diagrams generated interactively in EQS)
• BMDP Save Files [*.SAV] (data in BMDP System File format)
• Lotus [*.WK*] and dBase [*.DBF] Files as samples

The File Type dialog box area also provides filters for files of other types, namely Output [*.OUT], Covariance Matrices [*.COV], and Text [*.TXT].

The sample programs (Models) that EQS provides are called:

  
manul1.eqs   manul5.eqs    manul9.eqs   manul13.eqs
manul2.eqs   manul6.eqs   manul10.eqs   manul14.eqs
manul3.eqs   manul7.eqs   manul11.eqs 
manul4.eqs   manul8.eqs   manul12.eqs

To run a sample program, click File>Open, then choose the drive and directory path to the EQS directory (if not already open), then choose the File Type of *.EQS, then click on the desired program file. For example, if you choose manul7.eqs, it will appear in a Model (program) window. (Note that manul7.eqs calls an external data file, which must also be in the EQS directory when you run the sample.) You then click on Build EQS>Run EQS, and the program runs. Output appears on the screen, and when it is finished, a dialog box appears that asks if you want to open the output file that this Model run has just created.

References

1. EQS Structural Equations Program Manual, by Peter M. Bentler
   
2. EQS for Macintosh User's Guide, by Peter M. Bentler and Eric J.C. Wu
   
3. EQS for Windows User's Guide, by Peter M. Bentler and Eric J.C. Wu

Multivariate Software, Inc.
15720 Ventura Boulevard, Suite 306
Encino CA 91436

800/301-4456
818/906-0740
818/906-8205 (fax)

<sales@mvsoft.com> === http://www.mvsoft.com/

Reference 1. describes the EQS language and procedures for all platforms. The operations of EQS that are specific to each platform are described in References 2. and 3.

Current versions of these References are available only from the vendor.

USC Students, Faculty and Staff may use computers and documentation in the Public User Areas in Waite Phillips Hall, King Olympic Hall and Salvatori Computer Science Center, as well as the Leavey Library Information Commons (Ground Floor).

Consulting. The ITS Consultants may be familiar with the language and general operations of this software, but it may be necessary to make an appointment with a member of the full time staff in order to receive detailed help. Support of statistics software is the responsibility of the ITS Statistics Consultant with the participation of other full-time ITS staff. These people may be contacted through the ITS Customer Support Center as shown here.

Customer Support. USC students, staff or faculty who would like information about ITS Workshops or about obtaining site-licensed software or other computing-related questions should visit the Customer Support Center in Leavey Library Lower Commons, or call 213.740.5555, or send eMail to <consult@usc.edu>

Documentation. This document, and many others on a variety of topics, are available in the ITS Customer Support Help System, available on the World Wide Web at:

http://www.usc.edu/its/

You can find Statistics Software Help Documents through the search engine at this same URL, or go directly to them at:

http://www.usc.edu/its/doc/statistics/help/

Newsgroups. Another source of information, this one providing the opportunity to exchange thoughts with other users, is the newsgroup 'usc.comp.all.stat.users'. For more information about reading news, subscribing to newsgroups, and related topics, visit

  
http://www.usc.edu/its/doc/internet/news/