The ECB is designed to run on an IBM (or compatible) PC. In general, the greater the resources on your PC system (RAM, hard disk, etc.) the easier and faster it will be to operate the ECB. However, even '286' systems with floppy drives may be used (alt hough operation will be slower than with more powerful configurations).

The ECB system is comprised of one program file and several control files. The control files (NEL01.CDC; NEL02.CDC; NELS03.CDC) contain the question text and frequencies that are displayed by the ECB system, while the program file contains the software for running the ECB system (ECBNELS.EXE). Only the program file--system for running the ECB system--needs to be copied from the CD in order to use the system.

An ECB system can be run from several different PC set-ups or configurations. The ECB program file cannot be run from the CD itself; instead, it can be installed to a hard drive or a network drive (installation to a floppy drive is not recommended due t o the slow speed of such drives). The control files can remain on the CD or be copied to a hard drive or network drive. We recommend installing both the program and control files to either a hard drive or local network drive. Response is very slow when control files are run from the CD-ROM, particularly when the 'search' feature is used.

Determination of whether to install both the program file and control files or only the program file depends on whether or not adequate disk space exists to also install the system's control files from the CD-ROM.

Table 2.1 below summarizes the space needed for operating the fall 1994 NELS:88 BY-F1-F2 ECB.

Table 2.1--Space Requirements for the ECB System

Table 2.1 is important for users who are unsure if their PC has sufficient space to handle the NELS:88 ECB. The table shows that the ECB files total about 5.6 Megabytes of space but that less than 80 Kilobytes are consumed by the files that must be copied from the CD to your local disk -- only the ECBNELS.EXE (program file) must absolutely be copied from the CD; at installation the HELP (ECBWT.HLP) file is also copied from the CD.

The public-use datasets consume 163.2 Mb and the restricted-use consume 164.0 Mb of space on the CD. As discussed earlier in the first section of this guide, there are well over 6,000 variables in each of these datasets, and hence, SPSS-PC+ users need t o remember that this software has a limit of 254 variables (plus the Student ID) that can be included in any single analytic run. The discussion below provides some additional rules-of-thumb for calculating space required by SPSS/SAS statistical analyses .

In addition to the space needed for installing the ECB program and control files, you will need additional disk space for:

1. Storing output files generated by the ECB system, such as list files of selected variables, customized codebook files or the SAS-PC or SPSS-PC+/Windows program code files;
2. Creating statistical program system files; and,
3. Performing additional SAS-PC and SPSS-PC+/Windows functions other than initial creation of a system file, such as recodes of variables, statistical analyses, merges, sorts, and other basic data manipulation and analysis functions.

Space Needs for Storing Output Files. Program code files may be as small as 5K (or less) if only a few variables are selected, or as large as 60-80K if 200 or more variables are selected. The size of codebook files also depends upon the number of varia bles selected and can range from as small as 5K to more than 200K. Variable list files may range from 1K to about 25K.

Space Needs for Creating A System File. Estimating the size of the final system file produced from the SAS or SPSS program code can be accomplished by using the following formula:

NREC is the number of observations or data records on the file(s) from which you selected variables. Use the constant 24,500 NREC for all files except the base year and first follow-up teacher data files. For those files use NREC=44,000.

In most cases this formula will overestimate the needed space but it serves as a useful guide to the size of the final SAS-PC and SPSS-PC+ system files. What is not taken into account is the space needed by your statistical program to merge files and/or perform analyses (c. above). These functions will require additional space beyond that derived from the application of this formula.

1. Turn on your CD-ROM reader. Place the NELS:88 CD into your reader.
   
   
2. Build a subdirectory (on your hard drive or network drive) to hold the ECB software (program file or program, control and miscellaneous files). For example, to build a subdirectory on your hard drive, "C:", type:
   
   C:\>MD NELSECB
   
   

   Determine how much disk space exists; is there enough to also install the control and miscellaneous files? (about 6Mb for the program file, three control files and three miscellaneous files).
   
   

   Switch to your CD reader by entering its drive letter at the ">" prompt and hitting "Enter." (The drive letter "E:" is used in the instructions.)
   

   C:\>E:
   
   

   Copy files from directory "\ECB" on the CD to the subdirectory built in #2. For example, with the CD as "E:" and hard disk as "C:":
   

   >copy E:\ECB\ECBNELS.EXE C:\NELSECB

   >copy E:\ECB\EXTRACT.EXE C:\NELSECB
   
   If you want the ECB to run as fast as possible, copy all \ECB files to the directory you built in #2. This is the preferable mode of operation:
   

   >copy E:\ECB\*.* C:\NELSECB
   
   

   If you plan to store SAS-PC or SPSS-PC/Windows program code in a subdirectory that is different from the one built in #2, create it. For example:
   

   C:\>MD NELSPGM
   
   

   Change subdirectories so that the default subdirectory is the subdirectory built in #2.
   

   C:\>CD NELSECB
   
   NOTE: If you created another subdirectory (step # 6) other than the one containing the ECB program and control files, you can input this information to the ECB program via the INSTALLATION MENU (see step 10 below).
   

   C:\>CD NELSECB
   
   

   Execute the ECB software:
   

   C:\>ECBNELS
   
   

   The software will usually clear the screen and tell you that it cannot find "needed files". Press any key to engage the INSTALLATION MENU. (Skip the key press, if you are placed directly into the INSTALLATION MENU).
   
   

   Once at the INSTALLATION MENU, change all the drive and subdirectory (path) settings to fit your equipment. (Press function key 1 [F1] to get HELP). You may wish to print out \ECB\ECB.HLP to learn more about using the ECB software. However, the ECB does provide context sensitive help at any point in the software. You can always activate HELP by pressing F1.
   
   

   Part II--INSTALLATION MENU: Configuring Drives and Paths to Run the ECB Software

The first time you attempt to execute ECBNELS, the system will tell you it COULD NOT FIND NEEDED FILES. At this message, complete installation of the software by pressing any key except [ESCAPE] (since the [ESCAPE] key terminates the ECB) to get to the INSTALLATION MENU. You should see the Installation menu below:

Default drive & path C: [Drive and path to which ECB software was copied/ installed]

SPSS/SAS/Extract files drive and path code C: [Drive and path output files, e.g., SAS or SPSS program code file, codebook file, variable list file]

Compact disk drive E: [Drive letter for compact disk reader]

Warning BEEP for errors is ON [Warning beep may be 'toggled' on or off]

Toggle context sensitive HELP for errors OFF [HELP resulting from errors may be 'toggled' on or off]

Help [Gives specific information on installation options]

For the convenience of the user the above example includes a brief explanation of each option on the menu (below each option in "[ ]"). In the on-line ECB, these explanations are actually presented at the bottom of the menu and appear as you move throug h each selection. Move around the menu with left/right and up/down arrow keys or by entering the highlighted letter for each function (for example, keying in the letter "C" will take you to the Compact disk drive line). Press to exit the menu.

The first three menu choices are the most critical installation options. They tell the system where the ECB is stored (type D), where to write output files (type S), and where to find the compact disk with the raw data files (type C). The system cannot operate properly without instructions as to the location of the ECB software and CD.

In the present example, the system assumes that "C:" is your default drive, that is, the drive to which you copied the ECB program and control files. It is also assumed that "C:" is the drive to which your output files should be copied. Drive "E:" is a ssumed to be the name of your CD drive. If the default drives and path names displayed in the installation menu are not the drives and paths to which you copied the ECB software or to which you would like your output files copied, then you need to change the settings for these first three options.

In the present example, solely "C:" is specified as the default drive for the location of the ECB software files; however, based on the earlier example given, the ECB software files were actually copied to "C:\NELSECB. As such, you need to modify the de fault software drive and path code to reflect the exact location of the ECB software. You would change the current default "C:" to "C:\NELSECB."

Similarly, in the previous example you created a special subdirectory to which you would like your output files copied. Thus, you need to change the default output drive and path code from "C:" to "C:\NELSPGM." For the system to run, the full path name of the drive to which the ECB software has been copied or to which you would like your outfiles copied needs to be specified.

Finally, in the above example, the system is assuming that the letter of your compact disk drive is "E:". This is correct, according to the earlier example, and as such, you do not need to modify the current compact disk drive letter.

Additional Installation Features. On the Installation Menu you may also choose whether to hear a WARNING BEEP for errors that you make. When ON, errant keystrokes and other errors that are detected by the system cause the PC to sound a beep. This soun d may be toggled OFF if you desire. Simply moving into that menu option (with arrow keys or by selecting the highlighted "W" that takes you to that function while in the menu) and moving out again is a "toggle" that changes the setting (ON or OFF).

If you wish, the system will also provide HELP screens that are related to any errors you make -- it is "context-sensitive" in that the HELP instructions are pertinent to where you are in the system and the functions you are working with when the error occurs. You may "toggle" this feature OFF if you wish (as in installation example above). Note that when OFF, HELP is only provided when invoked by the F1 key.

You can access the Installation Menu at any time during an ECB session if you wish to inspect the default settings or change the default settings to new ones. You may activate the Installation Menu by entering I or ALT-N or from the main MENU.

2.5 Basic Features of the ECB System

The Main Menu Once the ECB software has been installed, it presents the main menu. From top-to-bottom, the screen displays the project title, the banner bar, the header bar, a list of variables, and the keystroke bar. These are described below:

Project Title identifies which database this ECB describes (in the current case it is "The National Education Longitudinal Study of 1988 Second Follow-Up", which indicates the final BY-F1-F2 version of NELS:88).

Banner Bar lists the major command groups of ECB functions. The highlighted letters are 'hot' keys that activate the commands. The entire set of commands is activated by function key 10 [F10].

Header Bar labels the columns of variable names and labels. In addition, the header bar identifies the module or section in which the highlighted variable is located. (For example, the second follow-up (F2) student file part 2 is identified on the head er bar as "F2ST2: F2 STUDENT PUB").

List of Variables displays each variable's name and a brief descriptive label. The 6000+ variables are ordered in modules by respondent entity (student, dropout, school, parent, teacher) and within these by survey wave (base year, first follow-up and se cond follow-up). The "List" function displays all variables that have been tagged. List is activated from the Main Menu, or it may be toggled by L and ALT-L.

Keystroke Bar describes the valid keystrokes (other than hotkeys) for scrolling through the list of variables. In addition, at the far right, a counter of the number of currently selected variables (or "tags") is displayed.

At the Main Menu, users may pursue the four major applications of the ECB:

1. The ECB displays information about each variable including:

• the wording of the questionnaire item from which the variable was derived or an explanation of a composite variable,
• for each discrete variable, numeric counts of the values are accompanied by both weighted and unweighted percents (Unweighted frequencies/percents are activated by U, ALT-U, Ins, or from the main Menu; Weighted frequencies/percents are activated by W, ALT-W, or from the main Menu),
• for each continuous variable, the valid range is presented as a label for all cases (instead of each value listed separately, which would involve an excessively long display),
• footnotes and comments are included for variables that have been recoded or suppressed in the public-use version of the data to protect confidentiality, or to notify users of potential bias from high item non-response in a variable, or to further eluc idate the meaning of a constructed variable (including pointing users to related constructs in the same or in different NELS:88 modules).

3. A subset of variables for extraction and analysis may be selected or "tagged."

4. The set of tagged or selected variables may be saved as output in the form of SPSS (PC+/Windows), SAS or Codebook Text.

Variable Names and Coding Conventions

Variable Names. Variable names begin with the survey wave for which the variable was created: "BY" = Base Year = 1988; "F1" = First Follow-up = 1990; "F2" = Second Follow-up = 1992. Certain school-level composites begin with the grade in which student s would be enrolled (including those who have dropped out) if they continued in normal grade progression -- for example, "G12" = Grade 12. Statistical weights include the string "WT" in the variable name. Case selection flags that should be used in tand em with statistical weights ordinarily include the same stem in the variable name. For example, F2QWT should be paired with the flag, F2QFLG (=1), in order to select and weight the twelfth grade cross-sectional student sample.

Missing Data Codes. A set of standard reserved codes are used in the NELS:88 datasets to help users differentiate reasons for missing data. These reserved codes and their meanings are:

• 6=MULTIPLE RESPONSE
• 7=REFUSED
• 8=MISSING
• 9=LEGITIMATE SKIP

Blanks may also appear as valid missing data indicators -- in the second follow-up student files, for example, blanks signify 'Non respondents and dropouts'. Data records are present on the file for these sample members even though particular data eleme nts are missing. Blanks are used to differentiate missings due to unit non-response from missings due to item non-response.

Within the frequency/percent windows for each variable, reserved codes are shown following the valid data codes. All reserved codes are displayed in brackets, {}.

Display for Continuous Variables. Continuous variables contain too many valid values to display in a frequency distribution, therefore, in the ECB display, continuous variables are assigned a code of {CONT} and are labeled with {minimum-maximum values a nd/or the mean-standard deviation}. (If the first (top) value presented in a percentage window is labeled within bracket, {}, the ECB software assumes the variable should be treated as continuous rather than categorical.)

The Search Feature

Searches may operate on one, two, or three information fields for each variable. All searches scan the variable names. Depending upon the user-defined toggles (further explained under SEARCH in the Command Set Glossary in Appendix E), you may choose in stead to search variable labels and variable descriptions.

Searches that are similar to Dbase/Paradox queries may also be accomplished to identify sets of variables. The procedure for query searches is:

• - Clearing all tags
• - Entering the desired Search String, and
• - Tag all matches.

Find next [CTRL - L] [Forward search will begin]

Search string is [Modify search string]

Labels search is ON [Toggle search of labels ON and OFF]

Description search is OFF [Toggle search of descriptions ON and OFF]

Tag all matches [Untags if currently tagged]

Import one file of tags [Loads a set of tags from one import file}

Combine two files of tags [Combine with AND or OR logic]

Advance to next tag [Moves down to next tagged variable]

Note that the default file of tags is C:\NELSECB\NEL.TAG. You may key in an alternate file name or hit to accept the default name. See the Output Menu (below) for how to designate a file for tagged variables. If you have not created a file of tags, when you instruct the system to IMPORT tags the system will beep to signal an error and report that it cannot find the file. When you attempt to Combine two files of tags, note that the tag must be in both files.

Users should also be aware that once begun, you cannot escape from a search-and-variable tag session. A search and tag session may consume several minutes or longer, depending on your equipment. Before initiating a search and tag session, take care to think through what you are entering and why, since you cannot abort a search of this kind in process.

Another caveat: when you tag variables (a check mark shows in the left column beside the variable name when you tag it), if you hit , the system moves you up to the top of the module and it may appear that your tagged variables have been lost. In fact they are not lost however -- the "# of tags" always appears in the lower right corner of your screen and you may refer to this counter at any time.

2.6 Edits for SAS and SPSS Output Code

Figure 2.2 shows the ECB Output Code Menu. You tell the system what kind of program code--SAS or SPSS (PC or Windows)--you are requesting in the Output Menu. Though the system will generate code with the appropriate commands for merging data files and producing frequencies and a system file, some editing of the code is required for the program to run without "warnings" or on a subset of cases (e.g., all women longitudinal cohort members) in addition to variables.

Special attention should be paid to the file names used within the code. While the file names embedded in the generated code should reflect the file names, drives and paths you specified in the Installation Menu and Output Menu (both the files to be use d as input, such as raw data files and output, such as the location to which you would like your output files copied), it is always prudent to check the file names used throughout the generated code before actually running it.

Another area in which editing on your part is needed is in selecting a particular sample/population of interest. Unless you specify through a subsetting or a selection statement that you would like to run your analyses or frequencies on, for example, th e twelfth grade cross-sectional sample, statistical techniques applied or data manipulations performed will be performed on the full BY or F1 or F2 sample (or some combination of files have been merged). More information on how to define meaningful NELS analytical populations is provided in Appendix B.

In general, users should be wary of the nuances of working with data stored on the NELS:88 ECB/CD-ROM. Like learning to use magnetic tapes, learning to use the NELS:88 ECB/CD-ROM well takes time--time to learn the peculiarities associated with working i n this particular medium and with this particular product. To reduce learning time somewhat keep in mind the troublesome peculiarities discussed above and the additional ones discussed below:

• Before running a SAS job using alpha-numeric variables (E.G. F2SUBJECT), users should delete format statements for the alpha-numeric variables.
• The help screen only works from the Main Menu. It cannot be accessed from the subscreens within the systems.

A -- SAS-PC program code [Creates file of SAS-PC extract program code]

S -- SPSS-PC program code [Creates file of SPSS-PC extract program code]

W -- SPSS for Windows include file [Creates include (*.inc) for SPSS for Windows

C -- Codebook text file [Creates text file codebook]

T -- Save file of TAGS for import [Creates file for Import (see Search Menu)

2.7 EXTRACT.EXE--A Handy Little Subsetting Program

In addition to subsetting variables through the ECB and cases through selection statements you place in the ECB-generated SAS or SPSS program code, you may subset both variables and cases with the separate program, EXTRACT.EXE (stored in \ECB\ on the CD) . EXTRACT operates through a codebook text file (NELCB.TXT by default). Using a codebook text file of particular variables that you generated, the EXTRACT program will write the codebook-text-file-selected variables out to an ASCII raw data file. EXTRA CT.EXE works from your DOS prompt.

If only a single data file (e.g., BY student) is being used, you may also set conditions to select cases. (But you must make sure that the attribute[s] on which you are subsetting cases [e.g., female eighth graders with high math test scores] is one of [are] the variables in the codebook text file [e.g., SEX, BY Mathematics Quartile). By entering EXTRACT at the MS-DOS prompt on your PC, a description of how to use the program will appear on your screen. The program is also described more fully in Appe ndix C of this manual.

Michelle Harvey, Library Assistant, Documents Center
The University of Michigan Library
CIC CD-ROM Technical Documentation Project

http://www.lib.umich.edu/govdocs/cicdoc/nels88/nels88c.htm