Systems Manual 1I Overview
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System Overview General The Statistical Solutions System for Missing Data Analysis incorporates the latest advanced techniques for imputing missing values. Researchers are regularly confronted with the problem of missing data in data sets. According to the type of missing data in your data set, the Statistical Solutions System allows you to choose the most appropriate technique to apply to a subset of your data. In addition to resolving the problem of missing data, the system incorporates a wide range of statistical tests and techniques. This manual discusses the main statistical tests and techniques available as output from the system. It is not a complete reference guide to the system. About this Manual Chapter 1 Data Management Describes how to import a data file, specifying the attributes of a variable, transformations that can be performed on a variable, and defining design and longitudinal variables. Information about the Link Manager and its comprehensive set of tools for screening data is also given. Chapter 2 Descriptive Statistics Discusses Descriptive Statistics such as: Univariate Summary Statistics, Sample Size, Frequency and Proportion. Chapter 3 Regression Introduces Regression, discusses Simple Linear, and Multiple Regression techniques, and describes the available Output Options. Chapter 4 Tables (Frequency Analysis) Introduces Frequency Analysis and describes the Tables, Measures, and Tests output options, which are available to the user when performing an analysis. Chapter 5 t- Tests and Nonparametric Tests Describes Two-group, Paired, and One-Group t-Tests, and the Output Options available for each test type. Systems Manual 1i Overview Chapter 6 Analysis (ANOVA) Introduces the Analysis of Variance (ANOVA) method, describes the One-way ANOVA and Two-way ANOVA techniques, and describes the available Output Options. Chapter 7 Plots An overview of the plots available in the system, such as: Scatterplot, Histogram, Bar Chart and Normal Probability Plot. Chapter 8 Tutorial A tutorial with examples you can work through. Appendices Includes references, error messages and data set information. Index Index contents, subject matter, topics. 2 Systems Manual 1. Data Management SYSTEM PREFERENCES AND READING/SAVING DATA SPECIFYING VARIABLE ATTRIBUTES GROUPING VARIABLES TRANSFORMING VARIABLES DEFINING VARIABLES THE LINK MANAGER Introduction This chapter introduces you to setting preferences for your output options, importing data from other applications, the attributes of a variable, cutting and pasting variables and cases in the datasheet, transformations that can be performed on a variable, and defining design and longitudinal variables. Also there is an explanation of the Link Manager that comprises a powerful set of tools that you can use for screening data. System Preferences You can set preferences for the output options for an analysis by selecting the View menu System Preferences option in the Main window to display the window shown below: Reading/Saving Data To import a file into the system select Open from the pull-down File Menu. The Open window is displayed where the file to be opened can be selected. Systems Manual 3i Chapter 1: Data Management Supported File Types See the Readme.txt for the most up to-date list of supported file formats and also Appendix D: External File Formats. The system can read any of the following file formats: Datasheet Lotus 1-2-3 Worksheet Frequency Table Paradox File Multiple Datasheet Quattro Pro Worksheet BMDP New System - Datasheet SAS for Windows/OS2 BMDP New System - Frequency Table SAS for Unix, SAS JMP BMDP Port File SAS Transport File ASCII - Delimited S-PLUS File dBASE or compatible SPSS Portable File Excel Worksheet and Excel for Office 2000 SPSS Data File FoxPro Stata File Minitab versions 8-12 Statistica version 5 Gauss File SYSTAT File If you enter a non-system file type in the File Name datafield, you will be prompted to specify a system file type: After pressing the OK button, the Import File Format window is displayed: Select a file format and click OK. The system copies the selected file format into the datasheet. 4 Systems Manual Chapter 1: Data Management Import an ASCII File If the selected file type is ASCII the following window is displayed: Import/Export The Import/Export selection buttons allow you to specify whether the file you want to import contains Variable Names in the first record: Data (default) The system reads the first record as variable data or values. Data plus Labels The first record is read as Variable Names and all subsequent records as data. Columns Separated By The Columns separated by selection buttons allow you to choose the character that separates the variables within the record. You can choose among comma, space, or tab. The system defaults to space. Rows Separated By The Rows separated by selections buttons allow you to choose the end of record marker that separates records within a file. You can choose among carriage return <CR>, line feed <LF>, or both <CR><LF>. The system defaults to <CR><LF>. Surround character variable with The Surround character variable with selection buttons allow you to specify characters to be used as “surround” characters for your alphanumeric (character) variables. ASCII text files can have single quote, double quote, or no surround characters. The system defaults to none. Missing Value Symbol The Missing Value Symbol selection buttons allow you to specify the characters to be used in the datasheet to represent missing values. Only one missing value code is allowed when importing ASCII. You can use a space as a character, but only when commas or tabs separate the data. You can also type in up to seven characters using any printing characters. The system defaults to an asterisk. Systems Manual 5i Chapter 1: Data Management Number of Rows Per Case The Number of rows per case datafield allows you to indicate the number of rows per case. For example, if each case takes up three rows of data, enter a 3 in the box. The system defaults to 1 row per case. Each case should have the fixed number of rows as specified. Import Variable Attributes Window The Import Variable Attributes window is displayed when you want to import any file including ASCII files. It displays a list of the variables in the file to be imported with their associated Statistical Solutions System type. You can change their type here before the file is imported into the system. To change an imported variable type: 1. Import a file. 2. Highlight a variable(s) in the Variable information list, and select a new type from the Type datafield. 3. Click on OK when you are satisfied with all your choices. The system imports your file and displays it in a new datasheet. NOTE: Generally the system does not handle date variables. When a date variable is detected, the system forces this variable to represent the number of days since Jan 1, 1900. You may also choose to read date variables as character strings or as continuous variables 6 Systems Manual Chapter 1: Data Management Specifying Variable Attributes In general, you will want to name your own variables rather than using default names Var1, Var2, etc. Most likely, you will also prefer to specify the type of data in the variables. You can name variables and specify variable type, role and format through the Specify Variable Attributes window. To display the Specify Variable Attributes window, double click on the name of a variable in the datasheet. Alternatively, you can choose Variable Attributes from the Variables menu to display the Specify Variable Attributes window. The Specify Variable Window is a tabbed window that lets you specify the attributes specific to each variable in your datasheet. It also lets you set cutpoints, modify categories and copy attributes. The four tabs are: Basic Attributes Specifies basic variable attributes. Set Cutpoints Groups continuous or ordinal variables. Modify Categories Groups nominal or ordinal variables. Copy Attributes Copies attributes from one variable to another variable(s). Specify Basic Attributes You can use the Basic Attributes window to change from the default Variable Name to any name not already assigned to a variable in the same datasheet. Each variable must be assigned a type. The type you assign to a variable affects its availability in certain plots and analyses. A variable can be considered nominal, ordinal, continuous, integer or character. The default is continuous. The terminology used is comparable to the Stevens classification system (see Variable Type later in this section). The tabs on the window change according to the type of variable chosen. Systems Manual 7i Chapter 1: Data Management Role The Role of a variable can be: None, Grouping, Case Frequency, or Case Label. The default is None, which you should interpret as any. Format The Format section of the Basic Attributes window provides fields for specifying the format of the values in the variable when displayed in the datasheet. Alignment The Alignment field lets you choose among Left, Right, Center, and Decimal. Field Width The Field Width of a variable refers to the number of characters that fit into one cell of the datasheet. You may want to specify a field width larger than that required by the data in the variable when you have a long variable name. Scientific Notation You can specify whether or not your variables are to be displayed in Scientific Notation. Decimal Places You can specify the number of Decimal Places that are to be the values for each variable. Decimal Places has a default of 2, with a range from 0 to 8. Show Group Names Use the Show Group Names option to show group names rather than original values for nominal, ordinal, continuous and integer variables. Double Precision Double Precision is applicable to Continuous variables only.