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11. NLTS2 Documentation: Data Dictionaries
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11. NLTS2 Documentation: Data Dictionaries
Prerequisites• Recommended modules to complete before viewing
this module 1. Introduction to the NLTS2 Training Modules 2. NLTS2 Study Overview 3. NLTS2 Study Design and Sampling NLTS2 Data Sources, either
• 4. Parent and Youth Surveys or• 5. School Surveys, Student Assessments, and Transcripts
10. NLTS2 Documentation Overview
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11. NLTS2 Documentation: Data Dictionaries
Overview Purpose Data dictionary contents File specifications
• Variable prefix• Missing values
Variable documentation Variable documentation details Parent/youth Part 2 documentation distinctions Transcript data documentation distinctions Supplemental documentation Closing Important information
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11. NLTS2 Documentation: Data Dictionaries
Purpose
• The data dictionary section of the documentation is the most detailed for individual data items.
• The data dictionary includes specific information about each item such as Which respondents are included in the data element if there is
skip logic applied. Documentation of any modification made to the data element,
such as a logical assignment to change a value. Variable names of corresponding items in other Waves.
• Users should refer to the data dictionary before specifying any analysis.
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11. NLTS2 Documentation: Data Dictionaries
Purpose• Why use the data dictionary rather than the data
collection instruments? Data collection instruments are extremely useful.
• Can be a quick reference for finding an item• Show the item in the context of other items• Contain the exact wording of questions that respondents were asked
However, only the data dictionaries describe• Complex skip logic, especially from CATI instruments• Data issues, such as an addition of response categories from one
wave to the next • Any programmatic modifications, assignments, or recoding of the
data, such as setting a value to yes if a prior response is yes
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11. NLTS2 Documentation: Data Dictionaries
Data dictionary contents
• There is a data dictionary for every data collection source within each wave.
• Every dictionary begins with a linked contents.• Links go to
File specifications. Variable descriptions by section or topic area.
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11. NLTS2 Documentation: Data Dictionaries
Data dictionary contents example
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11. NLTS2 Documentation: Data Dictionaries
File specifications
• The first section of the data dictionary is “File Specifications,” which lists The associated file name The data collection source The prefix for variable names in the file Linking variable (always “ID”) Missing values
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11. NLTS2 Documentation: Data Dictionaries
File specifications: Example
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11. NLTS2 Documentation: Data Dictionaries
File specifications
• Variable prefix The prefix for variable names in the file applies to most but
not all variables.• With a few exceptions, variables found in this file begin with the
variable prefix.– There are specialized variables that have another prefix structure,
such as wave-specific demographic variables.– Example: W2_Age2003 is the age of youth during the
Wave 2 Parent/Youth data collection and W2_Age2004 is the age of youth for the Wave 2 school data collection; the prefix is Wave 2.
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11. NLTS2 Documentation: Data Dictionaries
File specifications
• Missing values Can be found in this file.
• Note about missing values User-defined missing values specify why a variable is
missing. Missing values are excluded from calculations in procedures
unless the user specifies options to include them. Data were developed in SAS and converted to SPSS.
• There are differences in how missing values are defined and stored in SAS and SPSS.
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11. NLTS2 Documentation: Data Dictionaries
File specifications• Missing values in SAS
System default missing in SAS is a “.” User-defined missing values in SAS can have a value from
“.a” to “.z” Missing values in a numeric variable have a numeric value
in a SAS logical statement.• For example, the logical statement “If npr1B4 < 1” would include all
cases for which the value is “0”, a negative number, or a missing value.
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11. NLTS2 Documentation: Data Dictionaries
File specifications• Missing values in SPSS
SPSS system missing is a “.” in the data and appears as “System” in SPSS analysis output under “Missing.”
SPSS allows for three distinct user-defined missing values, fewer than SAS.
With the range option, users can define a range of missing values to work around the limitation of three distinct missing values.
Missing values are represented as negative numbers in the NLTS2 SPSS data.• -980 through -999 are in the missing values range.
Missing values in SPSS do not have a numeric value in a logical statement, unlike in SAS.• For example, “IF (npr1B4 < 1) B4New = 0.” would result in a missing
value in B4New if npr1B4 is missing.
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11. NLTS2 Documentation: Data Dictionaries
Variable documentation• After “File specifications,” the dictionary lists all variables in
tabular format.• The variables in the data dictionary are organized by section,
matching the sections in data collection instruments (source data).
• Within each section, there are two sets of variables. Variables that come directly from the data collection instruments. Variables created from source data within that section.
• Variable descriptions include Name, variable type, variable values, source(s), and information about
skip logic, assignments made, and corresponding variable names in other waves.
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11. NLTS2 Documentation: Data Dictionaries
Variable documentation
• Variables that come directly from the data collection instruments (source data) Variable names usually have the uniform variable prefix. Source data are drawn from the section, question number,
and subitems in the source instrument. It can be relatively straightforward to find an item in an
instrument and locate it in the dictionary. Example: variable name np4E2c
• The “np4” prefix is NLTS2 Parent/Youth Survey Wave 4.• The “E2c” is Section E of the Parent/Youth Instrument, Question 2,
subitem C.
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11. NLTS2 Documentation: Data Dictionaries
Variable documentation• Variables created from source data
Variables that are created using data from the associated section are listed at the end of the section.
Created variables typically have names that describe the variable rather than relate to a data collection source, but with the same prefix as the source variables.• Variable np3_JobCompNow is
[np3] Parent/Youth interview Wave 3 [JobCompNow] currently competitively employed
Collapsed variables, i.e., variables combined from two or more items, sometimes list all contributing variables in the name• Variable np4U8a_J15a is
[np4] Parent/Youth Wave 4 [U8a] question U8a [_] combined with [J15a] question J15a
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11. NLTS2 Documentation: Data Dictionaries
Variable documentation
• In addition to variables related to particular items from data collection instruments, there are some other key variables. Demographic variables that are used for many NLTS2
analyses and published Web tables Weights, including replicate weights Linking variable “ID” Preload, CATI, and/or sample variables
• The following slide provides a quick glance at the data dictionary with details in following slides.
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11. NLTS2 Documentation: Data Dictionaries
Variable documentation: Quick look
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11. NLTS2 Documentation: Data Dictionaries
Variable documentation: Formatting key• Bold text in the dictionary indicates a modification to
questionnaire categories as a result of coding and categorizing verbatim responses.
• Grey text indicates that there are no data for this item in this wave. For example, Question R1b was asked in Waves 2 to 4 but not in Wave
5; in Wave 5, R1b is shaded.
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11. NLTS2 Documentation: Data Dictionaries
Variable documentation details• Variable name
Name of the variable as it appears in the data file.
In this example, there is a series of variables for item np4F11b, np4F11b_a through np4F11b_h.• Each variable in the series is
listed separately.
Figure 1-A.
Note: See Figure 1, section C in Module 11 Supporting Materials.
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11. NLTS2 Documentation: Data Dictionaries
Variable documentation details• Source
Item from data collection source.
If multiple instrument sources, items from each data source listed.
This example comes from the question F11b, subitems a-g.
Figure 1-B.
Note: See Figure 1, section C in Module 11 Supporting Materials.
11. NLTS2 Documentation: Data Dictionaries
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Variable documentation details• Variable description
Describes the variable.• Often the text of the question from
the source instrument
Variable description corresponds with the variable label in the file contents.
Figure 1-C.
Note: See Figure 1, section C in Module 11 Supporting Materials.
11. NLTS2 Documentation: Data Dictionaries
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Variable documentation details• Variable description (cont’d)
In this example, the itemis described as types oflife skills training, the subitems are the individual types of life skills traininglisted in this question.
Subitems “a-g” come from the source and “h” is created.
Figure 1-D.
Note: See Figure 1, section C in Module 11 Supporting Materials.
11. NLTS2 Documentation: Data Dictionaries
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Variable documentation details• Variable type and values
Shows how the variable is coded and what the codes mean.
Variable type is numeric, date, or character.
The variable values match the variable’s associated format referred to in the SAS contents.
This example is a numeric variable with yes/no values.
Figure 1-E.
Note: See Figure 1, section C in Module 11 Supporting Materials.
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11. NLTS2 Documentation: Data Dictionaries
Variable documentation details
Describe any changes made to a variable List logic for making an assignment or
modification to an existing variable. Specify the logic for how new variables
were created. An assignment might increase or
decrease the base. In this example, assignments were made
to subitems np4F14_[a-g] to set values to “no” if np4F11a is “no.”
A new subitem np4F11b_h is created using values from np4F11a and np4F14a_f.
• Notes: Assignments, modifications, or validationsFigure 1-F.
Note: See Figure 1, section C in Module 11 Supporting Materials.
11. NLTS2 Documentation: Data Dictionaries
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Variable documentation details• Base: Which respondents asked
Logic is expressed as who isincluded, not who is skipped.
Explains varying n’s due toskip logic.
If “All respondents” is noted, itmeans no one is skipped.
In this example, the respondents asked this item were limited to those who had not been in secondary school in the past year and had specified this service since leaving high school.• However, in the notes column in the previous slide there was an assignment made.• Although they were not asked this question, those who were “no” to np4F11a were
assigned a “no” to np4F14_[a-g].
Figure 1-G.
Note: See Figure 1, section C in Module 11 Supporting Materials.
11. NLTS2 Documentation: Data Dictionaries
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Variable documentation details• Variable name by wave
Along with the variablename for the currentwave, correspondingvariable names are listedby all other waves.
There may be minor differences in the variables between waves, or an item may not have been asked in another wave.
In this example, there is no corresponding set of variables for this item in Wave 1, and the item is slightly different in Wave 5.
Figure 1-H.
Note: See Figure 1, section C in Module 11 Supporting Materials.
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11. NLTS2 Documentation: Data Dictionaries
Variable documentation details• Some of the columns noted above contain information not
found elsewhere. “Base” and “Notes” columns are key for understanding the
nature of a variable.• Provide documentation about who is included in an item and any
changes made to the data.• Particularly important when using CATI data with complex skip logic.
“Variable name by wave” is a resource for finding longitudinal items.• Provides wave-by-wave variable names.• Indicates if item not collected in a given wave and notes if item differs
in other waves.
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11. NLTS2 Documentation: Data Dictionaries Parent/youth Part 2 documentation
distinctions• Waves 2 to 5 Parent/Youth Survey has a Part 2 that is
completed by either the youth or the parent/guardian. Documentation for Part 2 in these waves includes all sources and
variable names. For each item, variables are listed in the following order: youth
item, the parent/guardian item, and a collapsed youth/parent item.
For collapsed items in cases where there is a value for both items, priority is given to the youth value.
Usually there is either a parent/guardian value or a youth value.
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11. NLTS2 Documentation: Data Dictionaries
Parent/youth Part 2 documentation: Quick look
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11. NLTS2 Documentation: Data Dictionaries
Parent/youth Part 2 documentation• The item is “Youth has done volunteer or community service in the past 12
months”.• np5P8 is the youth item, np5J4 the parent/guardian, and np5P8_J4 is the
combined youth/parent guardian item.• Data come from interviews (youth item P8 and parent item J4) and mail
questionnaires (youth A7a and parent Q20b).Figure 2-A.
Note: See Figure 2, section C in Module 11 Supporting Materials.
11. NLTS2 Documentation: Data Dictionaries
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Parent/youth Part 2 documentation• This example is a numeric variable
that has a yes or no value.• Notes: As we have seen in the
previous slide, data come from multiple sources. Youth interview and youth mail
questionnaire, parent/guardian interview, abbreviated interview, and mail questionnaires.
• Coding of combined item is described.
Figure 2-B.
Note: See Figure 2, section C in Module 11 Supporting Materials.
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11. NLTS2 Documentation: Data Dictionaries
Parent/youth Part 2 documentation• All youth respondents were
asked this question and all Parent Part 2 respondents were asked.
• There was no youth interview in Wave 1, but otherwise there are corresponding variable names for each wave for youth, parent/guardian, and combined.
Figure 2-C.
Note: See Figure 2, section C in Module 11 Supporting Materials.
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11. NLTS2 Documentation: Data Dictionaries
Transcript data documentation distinctions
• Transcript data are in multiple files. Each file is documented in a separate section in the
transcript data dictionary.• Files are either from source data or are summarized
data from course-level transcript data.• Files can have a single record or multiple records per
student depending on the type of transcript data.
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11. NLTS2 Documentation: Data Dictionaries
Transcript data documentation• Source data files
Overall: One record per student with any transcript data. By year: Multiple records per student with one record for every school
year recorded in transcripts. Course level: Multiple records per student with one record for every
course within a grading period.• Summary data files
Overall summary: One record per student with complete transcript data summarizing course taking across all grades attended.
By grade summary: Multiple records per student; one record for every grade attended summarizing course taking within a grade.
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11. NLTS2 Documentation: Data Dictionaries
Transcript data documentation: Quick look
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11. NLTS2 Documentation: Data Dictionaries
Supplemental documentation• Transcript dictionary
List of course codes and course categories Key to composite variable names in summarized data
• Parent/youth survey dictionaries Types of medications Job codes
• Assessment dictionaries Direct and alternate assessment references
• Cross-instrument data dictionary Decision rules for cross-instrument data
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11. NLTS2 Documentation: Data Dictionaries
Documentation summary
• The data documentation contains a wealth of information organized in a variety of ways.
• It is good practice to refer to the data dictionary before proceeding with analysis. Finding a question in a data collection instrument does not
provide enough information about that item. The data dictionary describes each item, including
information about skip logic and modifications made to variable values.
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11. NLTS2 Documentation: Data Dictionaries
Closing• Topics discussed in this module
Purpose Data dictionary contents File specifications
• Variable prefix• Missing values
Variable documentation Variable documentation details Parent/youth Part 2 documentation distinctions Transcript data documentation distinctions Supplemental documentation
• Next module: 12: NLTS2 Documentation: Quick References
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11. NLTS2 Documentation: Data Dictionaries
Important information NLTS2 website contains reports, data tables, and other
project-related information http://nlts2.org/
Information about obtaining the NLTS2 database and documentation can be found on the NCES website http://nces.ed.gov/statprog/rudman/
General information about restricted data licenses can be found on the NCES website http://nces.ed.gov/statprog/instruct.asp
E-mail address: [email protected]