CHAPTER 4 FREQUENCY DISTRIBUTIONS The SPPC "Frequency Distriution" procedure enables you to enter data from the keyboard or from disk files. If you are entering data from the keyboard you may use either grouped or ungrouped data and the procedure will guide you completely. The real power of this module arises from its ability to use data files that are stored on disk. Thus the remainder of this chapter is devoted to that use of the module. USING THE PROCEDURE The frequency distribution module of the SPPC is very easy to use. The first thing to do is select the "Frequency Distribution" option shown in the Master Menu of the SPPC program. When you do that, the frequency distribution procedure will then be called into your computer memory. The module will then ask you to enter the name of the data file that you wish to use. When entering the file name, be sure to include the disk drive and any necessary directory paths. This feature of the program means that you may fetch data files from any available diskette or any defined area on any hard disk. Just in case you are using data files stored on diskettes, the module will instruct you to insert your data diskette in the drive which you indicated when you provided the "filename". If your data file resides on a hard disk, just press the space bar. The module will then search for your raw data file. If it cannot find it in the location you specified, you will be so notified and then given another opportunity to enter the name of your file. If your data file is found, it will be described for you on screen. You must then indicate whether you wish to use the file that is described. Once you have indicated that you will use the located data file the module will then present you with the names of the variables within the data file and ask if you want to retain them. If you choose to retain a variable, the program will immediately begin to read your data from diskette. When it reaches the end of your data file it will query you as to whether you wish to continue reading more data from another file. If you do not choose to do so, the program will then ask if you wish to define your frequency distribution in terms of the number of class intervals or the size of each class interval. When you make that choice the program will immediately prepare your frequency distribution as well as an histogram of the distribution. When you indicate that you wish to choose another variable, the program will always begin with the variable that you selected last. It does that so that you may re-define the frequency distribution, if you wish, in terms of a different number of class intervals or a different class interval size. None of the frequency distributions will be sent directly to your printer. However, all of your results are saved for you as you work along. Then, when you exit the SPPC you will be given the option of reviewing your work on screen, printing it, or storing it in a disk file of your choice. DATA REQUIREMENTS The frequency distribution procedure requires the use of a raw data file that has been created for use by the SPPC program. If you are not familiar with the structure of such files, please read Chapter 2 of the User's Manual. NUMBER OF CASES There is no practical limit to the number of cases that you may have in a raw data file. The theoretical limit is 30,000 cases. You may fill an entire diskette with a single data file and you may continue a data file onto two or more diskettes. You may use as many diskettes as you like. ESTIMATED CASES Under normal circumstances, the second line of your data file will contain the number of cases, the number of variables, and the letter R. If you show the number of cases to be zero (0), the procedure will count the number of cases in your file and then report that number to you. CAUTION: You may NOT estimate the number of variables. NUMBER OF VARIABLES The maximum number of variables that you may have in any raw data file is 200. You may prepare a frequency distribution for any or all of them. SAMPLE OUTPUTS As an illustration we have prepared frequency distributions for three variables from the Longley data which are shown below. In this example we chose the option of defining the frequency distributions in terms of five class intervals. The output is shown below. Frequency Distributions The LONGLEY Raw Data: Byte Magazine (Nov. 1983), pp. 560-570. Var Name = Employed Mean = 65.317 Std Dev = 3.512 Cumulative Cumulative Interval Frequency Frequency Percent Percent 58.13-60.20 1 1 6.25 6.25 60.20-62.28 3 4 18.75 25.00 62.28-64.36 3 7 18.75 43.75 64.36-66.43 2 9 12.50 56.25 66.43-68.51 3 12 18.75 75.00 68.51-70.58 4 16 25.00 100.00 Histogram Interval Frequency 1 1 |************ 2 3 |*********************************** 3 3 |*********************************** 4 2 |*********************** 5 3 |*********************************** 6 4 |********************************************** Frequency Distributions The LONGLEY Raw Data: Byte Magazine (Nov. 1983), pp. 560-570. Var Name = GNP Mean = 387.698 Std Dev = 99.395 Cumulative Cumulative Interval Frequency Frequency Percent Percent 192.36-256.48 1 1 6.25 6.25 256.48-320.60 3 4 18.75 25.00 320.60-384.73 4 8 25.00 50.00 384.73-448.85 4 12 25.00 75.00 448.85-512.97 2 14 12.50 87.50 512.97-577.09 2 16 12.50 100.00 Histogram Interval Frequency 1 1 |************ 2 3 |*********************************** 3 4 |********************************************** 4 4 |********************************************** 5 2 |*********************** 6 2 |*********************** Frequency Distributions The LONGLEY Raw Data: Byte Magazine (Nov. 1983), pp. 560-570. Var Name = Unemployed Mean = 319.331 Std Dev = 93.446 Cumulative Cumulative Interval Frequency Frequency Percent Percent 176.16-234.88 4 4 25.00 25.00 234.88-293.60 3 7 18.75 43.75 293.60-352.32 2 9 12.50 56.25 352.32-411.04 5 14 31.25 87.50 411.04-469.76 1 15 6.25 93.75 469.76-528.48 1 16 6.25 100.00 Histogram Interval Frequency 1 4 |************************************* 2 3 |**************************** 3 2 |******************* 4 5 |********************************************** 5 1 |********** 6 1 |**********