PSPP USER GUIDE, Apuntes de Administración de Empresas

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PSPP Users’ Guide

GNU PSPP Statistical Analysis Software Release 0.8.

This manual is for GNU PSPP version 0.8.3, software for statistical analysis.

Copyright c 1997, 1998, 2004, 2005, 2009, 2012, 2013 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".

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Chapter 1: Introduction 2

1 Introduction

pspp is a tool for statistical analysis of sampled data. It reads the data, analyzes the data according to commands provided, and writes the results to a listing file, to the standard output or to a window of the graphical display.

The language accepted by pspp is similar to those accepted by SPSS statistical products. The details of pspp’s language are given later in this manual.

pspp produces tables and charts as output, which it can produce in several formats; currently, ASCII, PostScript, PDF, HTML, and DocBook are supported.

The current version of pspp, 0.8.3, is incomplete in terms of its statistical procedure support. pspp is a work in progress. The authors hope to fully support all features in the products that pspp replaces, eventually. The authors welcome questions, comments, donations, and code submissions. See Chapter 19 [Submitting Bug Reports], page 170, for instructions on contacting the authors.

Chapter 2: Your rights and obligations 3

2 Your rights and obligations

pspp is not in the public domain. It is copyrighted and there are restrictions on its distri- bution, but these restrictions are designed to permit everything that a good cooperating citizen would want to do. What is not allowed is to try to prevent others from further sharing any version of this program that they might get from you.

Specifically, we want to make sure that you have the right to give away copies of pspp, that you receive source code or else can get it if you want it, that you can change these programs or use pieces of them in new free programs, and that you know you can do these things.

To make sure that everyone has such rights, we have to forbid you to deprive anyone else of these rights. For example, if you distribute copies of pspp, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must tell them their rights.

Also, for our own protection, we must make certain that everyone finds out that there is no warranty for pspp. If these programs are modified by someone else and passed on, we want their recipients to know that what they have is not what we distributed, so that any problems introduced by others will not reflect on our reputation.

Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in e↵ect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone’s free use or not licensed at all.

The precise conditions of the license for pspp are found in the GNU General Public License. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. This manual specifically is covered by the GNU Free Documentation License (see Appendix A [GNU Free Documentation License], page 181).

Chapter 3: Invoking pspp 5

Specify this option more than once to produce multiple output files, presumably in di↵erent formats. Use ‘-’ as output-file to write output to standard output. If no ‘-o’ option is used, then pspp writes text and CSV output to standard output and other kinds of output to whose name is based on the format, e.g. ‘pspp.pdf’ for PDF output.

‘-O option =value ’ Sets an option for the output file configured by a preceding ‘-o’. Most options are specific to particular output formats. A few options that apply generically are listed below.

‘-O format=format ’ pspp uses the extension of the file name given on ‘-o’ to select an output format. Use this option to override this choice by specifying an alternate format, e.g. ‘-o pspp.out -O html’ to write HTML to a file named ‘pspp.out’. Use ‘--help’ to list the available formats.

‘-O device={terminal|listing}’ Sets whether pspp considers the output device configured by the preceding ‘-o’ to be a terminal or a listing device. This a↵ects what output will be sent to the device, as configured by the SET command’s output routing subcommands (see Section 16.19 [SET], page 155). By default, output written to standard output is considered a terminal device and other output is considered a listing device.

‘--no-output’ Disables output entirely, if neither ‘-o’ nor ‘-O’ is also used. If one of those options is used, ‘--no-output’ has no e↵ect.

‘-e error-file ’ ‘--error-file=error-file ’ Configures a file to receive pspp error, warning, and note messages in plain text format. Use ‘-’ as error-file to write messages to standard output. The default error file is standard output in the absence of these options, but this is suppressed if an output device writes to standard output (or another terminal), to avoid printing every message twice. Use ‘none’ as error-file to explicitly suppress the default.

‘-I dir ’ ‘--include=dir ’ Appends dir to the set of directories searched by the INCLUDE (see Section 16. [INCLUDE], page 153) and INSERT (see Section 16.16 [INSERT], page 153) commands.

‘-I-’ ‘--no-include’ Clears all directories from the include path, including directories inserted in the include path by default. The default include path is ‘.’ (the current directory), followed by ‘.pspp’ in the user’s home directory, followed by pspp’s system configuration directory (usually ‘/etc/pspp’ or ‘/usr/local/etc/pspp’).

Chapter 3: Invoking pspp 6

‘-b’

‘--batch’

‘-i’ ‘--interactive’ These options forces syntax files to be interpreted in batch mode or interac- tive mode, respectively, rather than the default “auto” mode. See Section 6. [Syntax Variants], page 29, for a description of the di↵erences.

‘-r’ ‘--no-statrc’ Disables running ‘rc’ at pspp startup time.

‘-a {enhanced|compatible}’ ‘--algorithm={enhanced|compatible}’ With enhanced, the default, pspp uses the best implemented algorithms for statistical procedures. With compatible, however, pspp will in some cases use inferior algorithms to produce the same results as the proprietary program SPSS. Some commands have subcommands that override this setting on a per com- mand basis.

‘-x {enhanced|compatible}’ ‘--syntax={enhanced|compatible}’ With enhanced, the default, pspp accepts its own extensions beyond those compatible with the proprietary program SPSS. With compatible, pspp rejects syntax that uses these extensions.

‘--syntax-encoding=encoding ’ Specifies encoding as the encoding for syntax files named on the command line. The encoding also becomes the default encoding for other syntax files read during the pspp session by the INCLUDE and INSERT commands. See Section 16.16 [INSERT], page 153, for the accepted forms of encoding.

‘--help’ Prints a message describing pspp command-line syntax and the available device formats, then exits.

‘-V’ ‘--version’ Prints a brief message listing pspp’s version, warranties you don’t have, copying conditions and copyright, and e-mail address for bug reports, then exits.

‘-s’ ‘--safer’ Disables certain unsafe operations. This includes the ERASE and HOST com- mands, as well as use of pipes as input and output files.

‘--testing-mode’ Invoke heuristics to assist with testing pspp. For use by make check and similar scripts.

Chapter 3: Invoking pspp 8

‘-O line-gutter=dimension ’ Sets the width of white space on either side of lines that border text or graphics objects. Default: 1pt.

‘-O line-spacing=dimension ’ Sets the spacing between the lines in a double line in a table. Default: 1pt.

‘-O line-width=dimension ’ Sets the width of the lines used in tables. Default: 0.5pt.

Each dimension value above may be specified in various units based on its sux: ‘mm’ for millimeters, ‘in’ for inches, or ‘pt’ for points. Lacking a sux, numbers below 50 are assumed to be in inches and those about 50 are assumed to be in millimeters.

3.3 Plain Text Output Options

pspp can produce plain text output, drawing boxes using ASCII or Unicode line drawing characters. To produce plain text output, specify ‘-o file ’ on the pspp command line, optionally followed by options from the table below to customize the output format.

Plain text output is encoded in UTF-8.

‘-O format=txt’ Specify the output format. This is only necessary if the file name given on ‘-o’ does not end in ‘.txt’ or ‘.list’.

‘-O charts={template.png|none}’ Name for chart files included in output. The value should be a file name that includes a single ‘#’ and ends in ‘png’. When a chart is output, the ‘#’ is replaced by the chart number. The default is the file name specified on ‘-o’ with the extension stripped o↵ and replaced by ‘-#.png’. Specify none to disable chart output. Charts are always disabled if your instal- lation of pspp was compiled without the Cairo library.

‘-O foreground-color=color ’ ‘-O background-color=color ’ Sets color as the color to be used for the background or foreground to be used for charts. Color should be given in the format #RRRR GGGG BBBB , where RRRR, GGGG and BBBB are 4 character hexadecimal representations of the red, green and blue components respectively. If charts are disabled, this option has no e↵ect.

‘-O paginate=boolean ’ If set, pspp writes an ASCII formfeed the end of every page. Default: off.

‘-O headers=boolean ’ If enabled, pspp prints two lines of header information giving title and subtitle, page number, date and time, and pspp version are printed at the top of every page. These two lines are in addition to any top margin requested. Default: off.

Chapter 3: Invoking pspp 9

‘-O length=line-count ’ Physical length of a page. Headers and margins are subtracted from this value. You may specify the number of lines as a number, or for screen output you may specify auto to track the height of the terminal as it changes. Default: 66.

‘-O width=character-count ’ Width of a page, in characters. Margins are subtracted from this value. For screen output you may specify auto in place of a number to track the width of the terminal as it changes. Default: 79.

‘-O top-margin=top-margin-lines ’ Length of the top margin, in lines. pspp subtracts this value from the page length. Default: 0.

‘-O bottom-margin=bottom-margin-lines ’ Length of the bottom margin, in lines. pspp subtracts this value from the page length. Default: 0.

‘-O box={ascii|unicode}’ Sets the characters used for lines in tables. If set to ascii the characters ‘-’, ‘|’, and ‘+’ for single-width lines and ‘=’ and ‘#’ for double-width lines are used. If set to unicode then Unicode box drawing characters will be used. The default is unicode if the locale’s character encoding is "UTF-8" or ascii otherwise.

‘-O emphasis={none|bold|underline}’ How to emphasize text. Bold and underline emphasis are achieved with over- striking, which may not be supported by all the software to which you might pass the output. Default: none.

3.4 HTML Output Options

To produce output in HTML format, specify ‘-o file ’ on the pspp command line, op- tionally followed by any of the options shown in the table below to customize the output format.

‘-O format=html’ Specify the output format. This is only necessary if the file name given on ‘-o’ does not end in ‘.html’.

‘-O charts={template.png|none}’ Sets the name used for chart files. See Section 3.3 [Plain Text Output Options], page 8, for details.

‘-O borders=boolean ’ Decorate the tables with borders. If set to false, the tables produced will have no borders. The default value is true.

‘-O css=boolean ’ Use cascading style sheets. Cascading style sheets give an improved appearance and can be used to produce pages which fit a certain web site’s style. The default value is true.

Chapter 4: Invoking psppire 11

4 Invoking psppire

4.1 The graphic user interface

The PSPPIRE graphic user interface for pspp can perform all functionality of the command line interface. In addition it gives an instantaneous view of the data, variables and statistical output.

The graphic user interface can be started by typing psppire at a command prompt. Alternatively many systems have a system of interactive menus or buttons from which psppire can be started by a series of mouse clicks.

Once the principles of the pspp system are understood, the graphic user interface is designed to be largely intuitive, and for this reason is covered only very briefly by this manual.

Chapter 5: Using pspp 12

5 Using pspp

pspp is a tool for the statistical analysis of sampled data. You can use it to discover patterns in the data, to explain di↵erences in one subset of data in terms of another subset and to find out whether certain beliefs about the data are justified. This chapter does not attempt to introduce the theory behind the statistical analysis, but it shows how such analysis can be performed using pspp.

For the purposes of this tutorial, it is assumed that you are using pspp in its interactive mode from the command line. However, the example commands can also be typed into a file and executed in a post-hoc mode by typing ‘pspp filename ’ at a shell prompt, where filename is the name of the file containing the commands. Alternatively, from the graphical interface, you can select File! New! Syntax to open a new syntax window and use the Run menu when a syntax fragment is ready to be executed. Whichever method you choose, the syntax is identical.

When using the interactive method, pspp tells you that it’s waiting for your data with a string like PSPP> or data>. In the examples of this chapter, whenever you see text like this, it indicates the prompt displayed by pspp, not something that you should type.

Throughout this chapter reference is made to a number of sample data files. So that you can try the examples for yourself, you should have received these files along with your copy of pspp. 1

Please note: Normally these files are installed in the directory ‘/usr/local/share/pspp/examples’. If however your system administrator or operating system vendor has chosen to install them in a di↵erent location, you will have to adjust the examples accordingly.

5.1 Preparation of Data Files

Before analysis can commence, the data must be loaded into pspp and arranged such that both pspp and humans can understand what the data represents. There are two aspects of data:

• The variables — these are the parameters of a quantity which has been measured or estimated in some way. For example height, weight and geographic location are all variables.
• The observations (also called ‘cases’) of the variables — each observation represents an instance when the variables were measured or observed.

For example, a data set which has the variables height, weight, and name, might have the observations:

1881 89.2 Ahmed 1192 107.01 Frank 1230 67 Julie

The following sections explain how to define a dataset.

(^1) These files contain purely fictitious data. They should not be used for research purposes.