This primer will introduce students to computer application in statistical analysis. The objectives are two-fold. First, to help students become familiar with the use of a Personal Computer (PC) system in a networking environment. Second, to encourage application of SPSS program in that environment to carry out several of the statistical procedures that will be discussed in class.
1. The Personal Computer (PC) Hardware
There are two basic types of computer hardware, viz., the Mainframe Computer, and the Personal Computer. The mainframe computer is housed on the fourth floor of the Meshel Building. Related peripherals include terminals (monitors and the attached keyboards) for gaining access to the Operating System (OS) or the Central Processing Unit (CPU), and the printers for printing hard copies of the computer outputs. These peripherals are located in Meshel and in other buildings throughout the YSU campus.
For our purpose the PC is the primary hardware. Several PCs are connected together to form a network. The keyboard, a mouse and the monitor are the primary physical components of a PC system. These are external devices. Internal components inside a PC include memory, disk drives, hard drive, and the CPU. Usually a PC, whether a stand-alone or part of a network, is connected to a desk printer to obtain hard copies of computer outputs. Thus, a PC system refers to a PC box with the internal components, a keyboard, a mouse, a monitor, and a printer.
The Keyboard and the Mouse are your input devices. You use the keyboard to type what you want the computer to do. The format in which you specify your requests is very rigid and stylized. Learning the format and the syntax rules of the Disk Operating System (DOS) is often the hardest part of learning to use the PC even in those situations where DOS is run under the windows graphical interface. There are many different models of computer keyboards but they all look like extended typewriter keyboards. Some have a few keys (notebooks and laptops), some have many extra keys, all have some keys labeled differently from a standard typewriter keyboard. But all keyboards have an area where alphabetic keys and the digits and the "standard" symbols (such as punctuation, $, %, &) are arranged as on a typewriter keyboard.
On some keyboards, the "carriage return" key is labeled "Enter"; on others, it is labeled with an arrow that points down one line and to the left; others have it labeled both ways. The carriage return key is also commonly a different shape from the corresponding key on a typewriter, but it is always in the correct general location at the right edge of the alphabetic keys.
The extra keys on the keyboard are used for special functions and are appropriately called the "function keys" (F1 through F10 or F12). They are essentially important to software developers. Many programs make extensive use of these extra keys. Ignore for now the mechanics of using these keys. All inputting will be done by using the "standard" keys and the mouse.
The mouse is the primary input device in windows graphical-interface environment. Entering a command is as easy as clicking the mouse on a specific menu item to select the desired command option.
The Monitor is the computer's primary output device. The
input that you enter via the keyboard or a mouse is usually echo printed
on the monitor. When you enter a command that produces output it is displayed on the
monitor, unless you direct the output to the printer.
2. Disk Operating System (DOS) and Windows Operating System (WinOS)
The usual way to organize information on a PC is to divide it into files. A computer file is conceivably much the same as a file that you would store on paper in a file cabinet. It is only the physical representation that is different: a computer file is stored on a magnetic disk.
Often we will want to do things to files: create them, edit them, read them, print them, erase them. To do so we need some way of referring to them: we will call this a file identification (or in short file id). For PCs the format for file id is FN.EXT where FN denotes FileName (at the most eight alphanumeric characters long) and EXT is an abbreviation for EXTension (at the most three alphanumeric characters long).
Prior to the introduction of WinOS (or simply Windows) by Microsoft, PC DOS was the program that would keep all parts of a computer functioning in harmony. After you boot the system by turning on the power on the PC and the monitor you would begin a session by using dedicated commands at the prompt (a line starting with C:\>) to communicate directly with DOS. A blinking cursor at the DOS prompt would indicate the readiness of the system to accept DOS commands for carrying out specific tasks. For example:
DOS command requesting a list of files that have been created previously.
e.g; DIR/P (to list files on C: drive ) or DIR/P A: (to list files on A: drive)
DOS command to rename a particular file.
e.g; REName BOB.CBS BOB.HW1
DOS command requesting that a particular file be erased.
e.g; DELete BOB.CBS
DOS command requesting that a particular file be printed.
e.g; Print BOB.CBS
Note: You must hit the enter key for DOS to accept the commands that you
issue at the prompt.
With Windows, it is not necessary to use the DOS commands. Because Windows is a graphical operating environment, it is much easier to carry out these operations by selecting the relevant command from a drop-down menu. For instance, if you open the File menu of any Windows compatible program/application, you can open a file from the disk by selecting the Open item, save a file to disk by selecting the Save item if you do not want to change the file name, or Save As if you want to save the file with a different name. Some operations such as copying/cutting a text for placement in another position or Windows application can be easily accomplished by first selecting the text, next right-clicking on the selected text, and then selecting Copy/Cut from the drop-down menu. Finally, go to the target position where you want to place the copied/cut text, click the right button of the mouse and select Paste to complete the operation. Of course, the same result can be achieved by using the copy (), cut () and paste () icons from the toolbar.
3. Accessing SPSS/win Program on the YSU Network
The version of the SPSS program that is installed on the YSU network runs under Microsoft Windows. To use the program it must first be loaded on to the local PC which is connected to the network server. These PCs are called network PC terminals and are found in all the labs on campus. Note that it is not possible to use SPSS/win remotely (from your home) via dial-up connection; you must go to a lab on campus in order to use the program.
In order to use the program in a lab, follow
Step 1: If the PC terminal is not already on, boot it by turning on the PC/machine and the monitor.
Step 2: Identify the SPSS icon from the Windows Desktop and double-click on it. This will load the SPSS program onto the local computer. The initial screen will show SPSS Processor is ready at the bottom left corner of the screen to indicate that the program is ready to accept the commands which are listed in the Command Menus (top row) beginning with FILE, EDIT, DATA, TRANSFORM, STATISTICS, ..., all the way to HELP.
Step 3: To exit SPSS/win, open the FILE menu and click on the Exit option. If you did not save the output to your diskette on the A:\ drive, the program will ask you to do so before ending your session.
Step 4: To exit WINDOWS, click on Start on the task bar, select the Shut Down... option, and then Shut down to log off the system. Note: You should only shut down the system if asked to do so by your lab instructor.
For further details about how to access this web site and the SPSS/win program from labs equipped with network PC terminals, read/print the information in Access From Network Terminals. You will also find additional instructions on how to create an SPSS/win data file as well as a description of the steps for doing and reporting Computer Exercises.
4. Using SPSS/win for Statistical Analysis
Details of the specific statistical procedures will be discussed during lectures. For example, in Econ 3781 the following SPSS/win commands in the STATISTICS and GRAPHS menus will be implemented:
GRAPHS for summarizing data graphically
SUMMARIZE for summarizing data numerically
COMPARE for Interval Estimation and Hypothesis Testing
ANOVA for Analysis of Variance
CORRELATE for Correlation Analysis
REGRESSION for Regression Analysis
TIME SERIES for Time series Analysis
Also, several of the statistical graphics listed under the GRAPHS menu will be used to visually examine patterns inherent in a body of data. Data entry and pre-processing as well as sampling will be performed by using the commands under the DATA and TRANSFORM menus. Refer to my manual "Learning Economics and Business Statistics With SPSS/win" for a detailed discussion of these and other SPSS/win commands and their applications.
4.1 Data Entry
The data entry screen is the default once the SPSS/win program is loaded into the computer memory. It has the appearance of a typical spreadsheet. The columns (j = 1, 2, 3, ...) contain the variable names while the rows ( i = 1, 2, 3, ...) indicate the case or observation numbers. The cell formed by an ith row and a jth column contains the value of the variable at the observation number. The value could be non-numeric (i.e.; a string) if the variable is qualitative or numeric if the variable is quantitative (discrete or continuous). But regardless of the of the data type, each cell must contain only one value.
Consider the Employee Database of TABLE 1. The variables Annual Salary, Age, and Experience are quantitative variables because their values are numeric; whereas Gender and Training Level are qualitative variables because they have non-numeric or string values. To create a file called employee.sav (the extension sav will be automatically added by SPSS/win when you save the file) you must execute the following command instructions:
Step 1: Double-click on var in the first column to open the Define Variable window .
Step 2: In the Variable Name box, type the variable name (e.g.; Salary) after deleting the default name var00001 (move the cursor to the box and use the delete or backspace key to do so). Note: The variable name must not exceed eight alphanumeric characters; this is a DOS restriction.
Step 3: Under Change Settings, open the Type window (i.e.; click on Type) and select the variable type from the list; for example, numeric for quantitative variable and String for qualitative variable. Optionally, you may also want to set Decimal Places to zero (i.e.; type 0 to replace the default value 2). Click on Continue to return to the previous window.
Step 4. Click on Labels to open the Define Labels window; in the Variable Label box, type a label that further describes the variable. For example, Annual Salary is an appropriate label for the variable salary.
Step 5: Click on Continue and then Ok to return to the data entry screen. Note that clicking on Cancel sequentially would also return you to the data screen. This is the command to use especially if you decide not to change the default settings or simply change your mind about changing a specific option value. Further hands-on-practice illustration of how to create a data set file in SPSS/win format will be presented in the computer lab.
For additional instructions on how to create a data file in SPSS/win format and the steps for doing/reporting computer exercises read/print the information in Access From Network Terminals.
4.2 The Command
SPSS/win does not require users to type in specific commands and their syntax using the keyboard. Rather, all that is required of the users is knowledge of how to use the mouse to open a menu. The menus and sub-menus contain the commands needed to carry out a specific task such as entering data or plotting a histogram. This primer uses a common convention throughout to illustrate the command sequence for accomplishing a specific task. For instance, to open an existing SPSS/win database file, say EMPLOYEE.sav which is already in your diskette in drive A, the command sequence means that you must do the following: First, click on the FILE menu to open it; next, select the OPEN option and at that window select DRIVES to open a submenu that lists all the available drives in the PC; then select A since your database file is on your diskette in that drive. You will immediately see employee.sav file highlighted if that is the only file or the first file on your diskette. Double-click on it or simply click on OPEN to open it. The variables names and part of the data set will instantly be visible on the screen. This means that the data set has been read into the computer memory with complete variable labels and ready to be used for statistical analysis.
To see a summary information about a specific variable, double-click on it to open the Define Variable window. Take GENDER for instance. Notice that the Variable Label reads EMPLOYEE GENDER, the Value Label reads F = Female, M= Males. Click on LABEL to see the details. Before you exit this window, click on Type to open that window. Notice that String is indicated as the variable type because is a qualitative variable (and so is in table 2 below). Click on Continue and then Okay to return to the data screen. Note that labeling the values of a qualitative variable makes it easy to read and understand the output of analysis.
Suppose you decide to create a new data file after opening an existing one. To clear the screen and start the data entry process, use the following command sequence: File/New/Data. A new data entry screen will appear and you are ready to define the variables and key in the data.
1. Table 2 below contains information about five employees of an administrative division of a company. Enter the data for the variables Gender, Salary, Education, and Experience. In the Define Variable window label Gender as Employee Gender, Salary as Annual Salary, Education as Education Level, and Experience as Experience in Years. Also, label Gender values as F = Females and M= Males; and Education values as HS = High School, BA=Bachelor, and MBA = Master of Bus. Adm. Note: You may not be able to type the names Education and Experience fully. Why?
Table 2: Employment/History Status of Five People
See the Histograms for the SALARY data and Basic Statistics for the Experience data in the Descriptive Statistics module of Learning Statistics with SPSS/win.
2. The data set below shows the Price-Earning (PE) ratios for 25 different common stocks of growth companies listed on the over-the-counter markets. Generate a histogram using the command sequence: . Describe the distribution. Also, compute and interpret the basic statistics using the Command Sequence and Example provided in the Descriptive Statistics module mentioned above.
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Copyrightę 1996, Ebenge Usip, all rights reserved.
Last revised: Sunday, January 07, 2001.