22/10/16. Data Coding in SPSS. Data Coding in SPSS. Data Coding in SPSS. Data Coding in SPSS

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1 DATA CODING IN SPSS STAFF TRAINING WORKSHOP March 28, 2017 Delivered by Dr. Director of Applied Economics Unit African Heritage Institution Enugu Nigeria To code data in SPSS, Lunch the SPSS The Data Editor window opens automatically when you start a session The Data Editor provides a convenient, spreadsheetlike method for creating and editing data files The Data Editor provides two views of your data: Data View: Displays the actual data values or defined value labels. 1 Variable View: Displays variable definition information 2 Data View: Akin to Spreadsheet with few distinctions 1. Rows are cases. Each row represents a case or an observation. For example, each individual respondent to a questionnaire is a case. 2. Columns are variables. For example, each item on a questionnaire is a variable. 3. Cells contain values. Unlike spreadsheet, cells in the Data View cannot contain formulas. 4. The data file is rectangular with no "empty" cells within the boundaries of the data file. For numeric variables, blank cells are converted to the system-missing value. For string variables, a blank is considered a valid value. The Data view is as seen on the next slide 3 Data View window: 4 Variable View Variable View contains descriptions of the attributes of each variable in the data file. In Variable View Rows are variables. Columns are variable attributes. The variable attributes Includes: Name: Variable name Type: Data type Width: Number of digits or characters Decimals: Number of decimal places Label: The Full Label of the Variable Values: Description of Variable categories Missing: User-defined missing values Columns: Column width Align: Data lignment Measure: Scale, Ordinal or Nominal Variable View window 5 6 1

2 To code data in SPSS, we must first prepare the coding template This means defining the variable properties using the Variable view window. Variable names must be unique; duplication is not allowed can be up to 64 bytes (64 characters in single byte language (e.g. English) and 32 in double byte language(e.g. Japanese, Chinese or Korean) the first character must be a letter or one of the #, or $ Subsequent characters can be any combination of letters, numbers, nonpunctuation characters, and a period (.) Variable names cot. Variable names cannot contain spaces A $ sign in the first position indicates that the variable is a system variable. not allowed as the initial character of a user-defined variable Variable names ending with a period should be avoided, since the period may be interpreted as a command terminator. Reserved keywords like: ALL, AND, BY, EQ, GE, GT, LE, LT, NE, NOT, OR, TO, and WITH. cannot be used as variable names. Variable names are case sensitive. In the Variable view window, click a cell under name and enter the variable name 7 8 Variable type Variable Type specifies the data type for each variable. By default, all new variables are assumed to be numeric. To Change it, click the cell under Type corresponding to the variable name. Click on after the Numeric to display this DB on the next slide containing the various data types Numeric. A variable whose values are numbers Comma. A numeric variable whose values are displayed with commas delimiting every three places and displayed with the period as a decimal delimiter. Variable type 9 10 Data type Cont. Dot. A numeric variable whose values are displayed with periods delimiting every three places and with the comma as a decimal delimiter. Scientific notation. A numeric variable whose values are displayed with an embedded E and a signed power-of- 10 exponent. E.g. 1.23E2 Date. A numeric variable whose values are displayed in one of several calendar-date or clock-time formats 11 Data type Cont. Dollar. A numeric variable displayed with a leading dollar sign ($), commas delimiting every three places, and a period as the decimal delimiter. String.(alphanumeric variable) A variable whose values are not numeric and therefore are not used in calculations. Restricted numeric. A variable whose values are restricted to non-negative integers. Select the data type, enter the width and the number of decimal places, ok The width and number of decimal places can also be adjusted directly on the variable view window 12 2

3 Variable Label. descriptive variable labels up to 256 characters (128 characters in double-byte languages Variable labels can contain spaces and reserved characters that are not allowed in variable names. Value Label: assign descriptive value labels for each value of a variable. useful if data file uses numeric codes to represent nonnumeric categories (for example, codes of 1 and 0 for male and female). Value labels are saved with the data file. You do not need to redefine value labels each time you open a data file. Value labels can be up to 120 bytes. Value Label Cont. SPSS assigns a default value of none to all new variable To change it, click on the cell under Values column along the variable row Click on the after the None in the cell to see the DB on the next slide. If the variable is Sex which measures the respondents gender, and its coded as 0 for female, 1 for male, this is communicated to the SPSS in the value label as follows. In the value box, enter 0. In the label box, type female, add. Repeat same for all the categories, ok Value Label Cont. Missing Values. defines specified data values as user-missing distinguish between data that are missing because a respondent refused to answer and data that are missing because the question didn't apply to that respondent. are excluded from most calculations Can contain up to three discrete (individual) missing values, a range of missing values, or a range plus one discrete value. Ranges can be specified only for numeric variables Missing Values cont. All string values, including null or blank values, are considered to be valid unless you explicitly define them as missing. Missing values for string variables cannot exceed eight bytes To define null or blank values as missing for a string variable, enter a single space in one of the fields under the Discrete missing values selection. Define missing Values. Make the Data Editor the active window. If Data View is displayed, double-click the variable name at the top of the column in Data View or click the Variable View tab. Click the button in the Missing cell for the variable that you want to define The default is none. If you want to change it, click the after the none in the cell to prompt the DB on the next slide Enter the values or range of values that represent missing data, ok

4 Define missing Values. Column (column Width) Specifies the width of the column. This can also be changed in Data View by clicking and dragging the column borders. Column width for proportional fonts is based on average character width. Depending on the characters used in the value, more or fewer characters may be displayed in the specified width. Column width affect only the display of values in the Data Editor. Changing the column width does not change the defined width of a variable Variable Measures: scale (numeric data on an interval or ratio scale): values represent ordered categories with a meaningful metric, so that distance comparisons between values are appropriate Nominal: values represent categories with no intrinsic ranking e.g. region, zip code, and gender state of origin Ordinal: values represent categories with some intrinsic ranking (for example, levels of service satisfaction from highly dissatisfied to highly satisfied) use numeric codes to represent ordinal data. Why? Role: Assigns predefined roles that can be used to pre-select variables for analysis Input. The variable will be used as an input (e.g., predictor, independent variable). Target. The variable will be used as an output or target (e.g., dependent variable). Both. The variable will be used as both input and output. None. The variable has no role assignment. Partition. The variable will be used to partition the data into separate samples for training, testing, and validation Role cont: Split. Included for round-trip compatibility with IBM SPSS Modeller. Variables with this role are not used as split-file variables in IBM SPSS Statistics. By default, all variables are assigned the Input role. This includes data from external file formats and data files from versions of SPSS Statistics prior to version 18. Role assignment only affects dialogs that support role assignment. It has no effect on command syntax. To assign role, click the Input cell along the variable row in the variable view window, select the role. Applying variable definition attributes to multiple variables: one or more attributes of a variable can be copied and applied to one or more variables. Basic copy and paste operations are used to apply variable definition attributes. Copy a single attribute (for example, value labels) and paste it to the same attribute cell(s) for one or more variables. Copy all attributes from one variable and paste them to one or more other variables. Create multiple new variables with all the attributes of a copied variable

5 Generating multiple new variables with the same attributes In Variable View, click the row number for the variable that has the attributes that you want to use for the new variable. From the menus choose: Edit > Copy Click the empty row number beneath the last defined variable in the data file. From the menus choose: Edit > Paste Variables... In the Paste Variables dialog box, enter the number of variables that you want to create. Enter a prefix and starting number for the new variables. Click OK. Changing the default variable view Customize Variable View to control which attributes are displayed by default in Variable View and the order in which they are displayed. From the menus, choose: Edit > Options: The DB on the next slide will appear Changing the default variable view Changing the default variable view Click the Data tab: The DB Will change to: Changing the default variable view Click Customize Variable View to get the DB Below Creating Custom Variable Attributes: To create new custom attributes: From the menus in Variable View, choose: Data > New Custom Attribute... Select (check) the variable attributes you want to display. Use the up and down arrow buttons to change the display order of the attributes

6 Creating Custom Variable Attributes: Drag and drop the variables to which you want to assign the new attribute to the Selected Variables list. Enter a name for the attribute following the same rules as variable names. Example is attribute that identifies the type of response for survey questions single selection, multiple selection, fill-in-the-blank Enter a value for the attribute or leave it blank and then enter values for the variable(s) in Variable View. 31 Creating new Variable Using a wide variety of mathematical functions, you can compute new variables based on highly complex equations From the menus in the Data Editor window choose: Transform > Compute Variable... To get the DB on the next slide Assuming we want a variable log(income) which is log to base 10 of our income variable; Fill the target variable with logincome not log(income). Why? Enter the formula log10(inc) on the numeric expression box, ok This will add a new variable named logincome in the data list 32 Creating new Variable This is used to identify suspicious and invalid cases, variables, and data values in the active dataset. The procedure produces lists of variables, cases, and data values that fail various checks, counts of violations of single-variable and crossvariable rules, and simple descriptive summaries of analysis variables. To Validate Data From the menus choose: Data > Validation > Validate Data..., to show the Validate data DB on the next Slide Validate data DB Select the Variable to Validate: Gender in our own case Click the arrow pointing to Analysis Variable Box to send the variable to the box Select the case identifier variable: Household ID in our own case Click the arrow pointing to the Case Identifier box to send the variable to the box Click on the Single-Variable rule button on top of the DB to get the DB on the next slide

7 Click on this to get the next DB 1. Click on new 2. Change this to Numeric 3. Fill these boxes with 0 and 1 4. continue Click ok 5. Click apply box