CHAPTER 1 THE SPPC USER'S MANUAL Welcome! And congratulations on your decision to purchase and use one of the world's simplest and easiest statistical programs. No longer will you have to master complex instructions, batch files, and all the other "management" chores that are often imposed on you by a variety of computer programs. All facilities of the SPPC program are available to you with a minimum of effort on your part and nearly all of it's very powerful features are only a few keystrokes away! We've made a concerted effort to make the SPPC so 'User Friendly' that you hardly ever need to use the User's Manual. Now that we've told you how pleased we are that you have chosen to use the SPPC, let us tell you about the program and what you can do with it. The Statistical Package for the Personal Computer or SPPC program is a fully interactive statistical package that enables you to enter, manage, and analyze both simple and complex sets of data. You may store very large sets of data on a diskette or hard disk file and then use one or several of the available procedures to analyze your data. The SPPC program allows you to conduct a very wide range of statistical procedures. For example, you can prepare frequency distributions, prepare crosstabs, calculate simple descriptive statistics, conduct a wide range of parametric and non-parametric hypothesis tests, obtain numerous confidence intervals, conduct several types of simple and complex regression analysis, compute probabilities associated with a variety of continuous and discrete distributions, and MUCH more. USER FRIENDLY A truly unique feature of the SPPC is its very high degree of user friendliness. Moreover, the SPPC is one of the world's simplest and easiest to use statistical packages that you can obtain. Everything is presented to you in the form of simple menus and on-screen instructions and you will never see a screen that does not provide some cue as to what you should do next. Thus, it is nearly impossible to get "lost". In addition, the program presents specialized assistance any time you see 'Help = ?' on your screen. At those points just press the ? key (i.e., Shift ?) and special help will be provided. These very extensive instructional and "help" functions all but make a User's Manual unnecessary. Yet, the program will print a complete User's Manual for those who like to read hard copy. THE SPPC OUTPUT DISK In addition to the extensive and powerful statistical functions of the SPPC, it contains a very special output feature that professional researchers and statisticians will come to enjoy. It is a special feature that enables you to capture virtually all of your output in a form which you can later edit by using your own word processor. We think this is a critical facility because it enables you to move any or all of your statistical outputs into any report or document that you may be preparing. Here's how it works. Anytime that you use the SPPC program (no matter what you do!), it creates a special file named "printer.wrk" file. You will never see that file but we want you to know about it! The program prints virtually all of your output onto the "printer.wrk" as ordinary text. Then, when you are finished with a computer session and attempt to exit from the program, it will present you with an option to send your output to (1) the screen, (2) the printer, or (3) a disk file of your choice. Moreover, you can use any or all of the three output options. For example, you could review your output on screen, then print it, and then send it to any disk file of your choice! Why is this feature so important? If you send your output to a disk file, you can then edit that file with your favorite word processing program and with enormous ease move the contents of your statistical outputs into research reports, statistical reports and summaries, and (if you are a student) homework assignments! Suppose, for example, that you have some work to do. First you compute some probability statistics. Then you run some frequency distributions. After that you compute some descriptive statistics, and finally you conduct a couple of multiple regression analyses. All your outputs will be saved for you! Now suppose that you need to include some or all of those statistical results in a special report (or homework assignment) that you are preparing. When you exit the program you can choose the option to save your work onto a separate diskette. Suppose for example, that you want to save all your work on a diskette in Drive A in a file named MYSTATS. If so, choose the option to save your work on a separate disk file and then give the program (when it asks for it) the name A:MYSTATS. That's all there is to it! You can then use your word processor to edit the MYSTATS file and incorporate your statistical outputs into the report you are preparing. IMPORTANT NOTE: If you are using a dual floppy system, you MUST prepare a formatted blank floppy diskette and label it as your SPPC OUTPUT DISK. The program will instruct you as to when you should put the SPPC OUTPUT DISK in Drive B. If you are using a hard disk system you do not need the SPPC OUTPUT DISK. LIMITATIONS: If you are using a dual floppy system and you have a lengthy session on the computer, you could easily fill up an entire SPPC OUTPUT DISK. That's a pretty big output file! Naturally, you would not want to run out of space so run a few simple jobs, save the results to a disk file and think about how much room is required by the various jobs that you will be running. With a little experience you will get a feel for the amount of disk space you are using for your outputs. WARNING! We really dislike giving "warnings" because they sound so ominous! Nonetheless, we want you to know that the SPPC program ALWAYS begins a new session with a completely empty "printer.wrk" file. Thus, if you do not save your outputs by printing them or storing them in a disk file, they will be erased. That's not really so terrible because the program is so easy to use that you could simply repeat any anaysis that you like. However, why go to that bother when it is so easy to save your results? We just wanted you to know what happens. NUMBER OF CASES The SPPC program is capable of processing a truly huge number of cases. In fact, it is just as powerful in that regard as ANY mainfram giant that you will ever encounter. It will process an UNLIMITED number of cases! If you have a very large number of cases in a set of data you may wish to store the data in two or more files having different names. If you wish to do that, the SPPC modules that accept raw data files will also accept continuation files. You may use as many continuation files as you wish and they may continue over two or more diskettes. There is NO LIMIT to the number of 'cases' or data records that may be processed and there is no limit to the number of continuation disk files or diskettes that you may choose to use. SIMPLE KEYBOARD INPUT Although the real power of the SPPC is its ability to process truly huge raw data files, it also contains numerous procedures for which data entry is so simple that it is done from the keyboard. Thus, you've got the best of both worlds -- disk file and keyboard input! NUMBER OF VARIABLES The SPPC will also handle some pretty big jobs when it comes to processing large numbers of variables. It will input any raw data file containing up to 200 variables and then allow you to select any subset of 51 or fewer of them for actual processing. Naturally, this is rather small when compared with the huge capacities of mainfram statistical packages. However, these variable limits are quite adequate for the overwhelming majority of analyses that most will need to perform on a microcomputer. SPEED AND ACCURACY The SPPC is VERY fast! If you are using a high speed math chip on your system, the SPPC program automatically detects and uses it. However, it also employs very efficient computing algorithms in those environments that do not use the math chip. In a comparative test we found that a popular competitor that's been around for years required 2.5 minutes to read a raw data file of 362 cases and compute a 15x15 correlation matrix -- using the math chip, a 4.77 MH clock and a hard disk. The SPPC did the job in 1.25 minutes -- TWICE AS FAST! Yes, with a math chip and hard disk the SPPC gets HOT! It's TORRID on an AT or equivalent computer using faster clocks! Ummm, it really sings with a 10MH clock and a math chip! The SPPC is also very accurate. It nearly always provides 13 decimal positions of internal accuracy and is capable of handling unusually difficult computational tasks. For example, it correctly solves the Longley Data regression problem! We have made special efforts to provide you with superior accuracy when using the "Probability Funtions" option in the main menu. Specifically, the functions which compute t- and F-probabilities are rather slow but they are extremely accurate. Lots of heavy number crunching is involved. Other procedures in this statistical package use a very fast algorithm for computing t- and F-probabilities but their accuracy should not be trusted beyond the third decimal position. In short, we've made some trade-offs between speed and accuracy. The reason we mention this trade-off here is to let you know that the "Probability Functions" procedures are very accurate. Thus, if you are "nervous" about t- and F-probability estimates obtained from other procedures, or you just want to make sure you have five decimals of accuracy in your t- F-probabilities, you can always use the "Probability Functions" to get that. THOSE BEAUTIFUL SIMPLE STATISTICS!! We think that one of the most powerful and attractive features of the SPPC is the inclusion of a large number of truly simple statistical procedures. You know, the ones you'd like to have and need all the time but can't find on other microcomputer or your mainframe packages? For example, how many times have you read a journal article and doubted the author's computations for, say, a t-test or Chi-square statistic? How many times have you wanted to compute a confidence interval around some descriptive statistic but didn't because it was too much trouble or you couldn't take the time? These are things you can easily calculate on your pocket calculator, but that means getting out the calculator, plugging in the formulas and then entering the data to get the solution-check you wanted. The SPPC takes all that agony out of your scientific reading and all the other simple statistical chores that you need handily available. The SPPC program presently includes a large number of these simple "convenience" procedures and even more will be added in the future. We love them and so do others who work with statistical problems. Naturally, we can't pretend that all of them you may want are present in the package. However, we shall be delighted to occasionally serve as your personal statistical programmer! Yes, indeed. If you will write to the publisher and suggest the addition of your favorite statistical goodie, we just might be able to include it for you. If we do and if you've purchased the appropriate module, you'll get the upgraded module free! PURCHASE WHAT YOU NEED As you well know, many systems require that you purchase an entire package or none at all. Not so with the SPPC. You may choose among the procedures that are available so that you can put together the package that suits your needs and pocketbook. Speaking of pocketbook, each one of the SPPC modules is priced with considerable modesty (print an order form to obtain prices for each of the modules). HARD DISK MULTI-USER INSTALLATION If your office environment or school is structured to provide a hard disk computer system for use by several users you may easily install one copy of the SPPC program on the computer for use by each user. PLEASE NOTE: This is NOT a license to purchase one copy of the program for use by multiple personnel. It is a procedure for sharing equipment only. INITIAL INSTALLATION If you have not yet installed the SPPC program on your hard disk, we recommend that you do so immediately. Just follow the procedures that are described in the README procedure of the SPPC Disk 1. Once you have installed the program on your hard disk you may use the following procedures any time you wish. ADDING A USER TO THE SYSTEM In order to add a user to the system, carry out the following procedures. We shall illustrate with an example in which a user by the name of Dr. Timothy J. Johnson is to be added as a new user. 1. Dr. Johnson must first purchase his copy of the SPPC program. Dr. Johnson may then be added as a user of the SPPC program that has been installed on your hard disk system. 2. Dr. Johnson must now be given a unique USERID of eight characters or less. In this example, you might choose to use a USERID of TJJOHN. Once you have decided upon a USERID issue the commands, CD\ ADDSPPC USERID where USERID is replaced with the one of your choice for the user to be added to the system. In this example, you would issue the commands, CD\ ADDSPPC TJJOHN The ADDSPPC procedure checks your hard disk first to determine whether another user is already using the USERID that you selected. If the same USERID is already in use, the procedure will so inform you. You will then have to choose another USERID for the new user that you are adding to the system. If the USERID you selected is not currently in use, it will be added to the system and the new user will then be able to use the SPPC program that you installed on your hard disk. USE OF THE SYSTEM Once someone has been added as a user of your hard disk system, he or she may set up the system for their use at any time. The user may do that by issuing the following commands, CD\ SETSPPC USERID If the user is a legitimate user of the SPPC program, the SETSPPC procedure will immediately prepare the program for the individual's use and then begin execution. In this example, Dr. Johnson is now installed as a user of the hard disk copy of the SPPC program. He may now set up the system for his use by issuing the commands, CD\ SETSPPC TJJOHN REMOVING A USER FROM THE SYSTEM Just as you may add users to your hard disk system, you may remove them. To do that, issue the commands, CD\ DELSPPC USERID NEXT STEPS The next chapter of the User's Manual explains how to prepare and use very large data files. It is therefore a very important chapter and we urge you to read it carefully. All subsequent chapters describe the various statistical procedures that are available for your use.