Chapter 1. Manage the data

Transcription

1 1.1. Coding of survey questions Appendix A shows a questionnaire with the corresponding coding sheet. Some observations of the selected variables are shown in the following table. AGE SEX JOB INCOME EDUCATE DISTRICT COUNTRY The data set of 40 observations of the selected variables is saved in three types of format SPSS data file, Excel spreadsheet and ASCII data file. Remarks One observation per row Each column represents one variable (SPSS data file and Excel spreadsheet) Sometimes, information for a particular variable is not available for some reasons. You can assign values to the variables when information is missing. Scale of data A scale of a tool or mechanism by which individuals are distinguished on the variables of interest to our study, in some form or the other. Nominal scale is one that allows the researcher to assign subjects to certain categories or groups. e.g. gender, country of residence. Ordinal scale not only categorizes the variables in such a way as to denote qualitative differences among the various categories, it also rank-orders the categories in some meaningful way. With any variable for which the categories are to be ordered according to some preference, the ordinal scale would be used. The preferences would be ranked and numbered 1, 2 and so on. Column number in survey.dat Marjorie Chiu,

2 Interval scale allows us to perform certain arithmetical operations on the data collected from the respondents. It also measures the magnitude of the differences in the preferences among the individuals. E.g. scale points, temperature. Ratio scale overcomes the deficiency of the arbitrary origin point given to the interval scale, in that it has an absolute zero point which is a meaningful measurement point. e.g. weight Retrieve the SPSS data file (survey.sav) Example 1 Open Specify the path and the filename (survey.sav) of type SPSS Get the data from an Excel spreadsheet (survey.xls). Open Specify the path and the filename (survey.xls) of type Excel. If the spreadsheet has variable names already, click the box for Read Variable ame. If necessary, you may indicate the range of cells in spreadsheet by input the cell names of top left corner cell and bottom right corner cell, separate them by a colon (A1G41) Read the data from an ASCII data file (survey.dat) Read Text name survey.dat Fixed width Insert the line break at appropriate position and change the variable name, label, values, measure etc in the "Variable View". Marjorie Chiu,

3 Name Start column End column type Age 1 1 Numeric Sex 2 2 Numeric Job 3 4 Numeric Income 5 5 Numeric Educate 6 6 Numeric District 7 7 Numeric Country 8 8 String Remarks Each variable is recorded in the same column location on the same record for each case in the data file. By default, SPSS assumes one record per case for fixedformat data. You must use the RECORDS subcommand if there is more than one record per case. When we define the variable name The name must start with a letter. The remaining characters can be any letter, any digit, a period or the symbols such #, or $. The maximum length of the name is 8 characters. No blanks or special characters such as, &,!, and * can be used. No duplication of variable names is allowed. The following keywords cannot be used as variable names since they have special meaning in SPSS. ALL AND BY NOT OR TO WITH EQ GE GT LE LT NE The most common types of variables are numeric and string (alphanumeric). Numeric variables contain only numbers. A string variable can contain a combination of letters, numbers and special characters Input the data in SPSS Editor Key in the data into the View of SPSS Editor and define the variables in the Variable View. We can label a variable to assign an extended descriptive label to variables. The description of values can be provided by value label. When the values are defined as a string, use double quotations to quote the values Define the variables Example 2 (miles) Marjorie Chiu,

4 The following table gives the quarterly figures of the aircraft miles (millions) flown by the ABC airlines from 1986 to Define the variable and input the data Input the data in sequence and then switch to the "Variable View" ame miles Type numeric, decimal0 Label aircraft miles (millions) Define the date Define dates Cases are Years, quarters First case is Year 1986 Quarter 1 Remember to save the file as miles.sav Manipulation Using subset of cases Select Cases State the method of select cases. For example, analyze the male group only of the survey data. Transformation of data Transform Compute Variable Define the new variable and key in the numeric expression of the computation. For example, evaluate the difference of aircraft miles in successive time periods. diff = miles lag(miles) recoding Transform Recode Into Different Variables Marjorie Chiu,

5 Select the input variable and specify the output variable, then define the old and new values of the numeric variable and the output variable. For example, combine the age groups and of the file survey.sav to form a group and the grouping of other age groups are unchanged. Age Original grouping New grouping & above Save the data file in SPSS When the SPSS Editor is active, we can save the data file. Save Specify the location and file name of the data file. Marjorie Chiu,

6 Exercise 1 Question 1. input and retrieval Popular car data (bsm1) Input the data in the following table in a SPSS data file format. MANUFAC MODEL TYPE MINPRICE MAXPRICE MPGCITY MPGHIGH CYLINDR LITERS HPOWER Acura Integra Small Acura Legend Midsize Audi 90 Compact Audi 100 Midsize BMW 535i Midsize Buick Century Midsize Buick LeSabre Large Cadillac DeVille Large Cadillac Seville Midsize Chevrolet Cavalier Compact Chevrolet Corsica Compact Chrysler LeBaron Compact Chrysler Imperial Large Dodge Colt Small Dodge Dynasty Midsize Dodge Stealth Sporty Eagle Vision Large Ford Festiva Small Ford Escort Small Ford Tempo Compact MANUFAC = Manufacturer MODEL = Model TYPE = Type of car MINPRICE = minimum price in US$1000 MAXPRICE = maximum price in US$1000 MPGCITY = miles per gallon for city driving MPGHIGH = miles per gallon for highway driving CYLINDR = number of cylinders LITERS = engine size in litres HPOWER = maximum horsepower Question 2. Cod catch data (cod) The cod catch time series data (weight in tons) for the is listed in the following table Month Input the data and define the variable and the date. Marjorie Chiu,