User Guide for the TIMSS International Database.pdf - TIMSS and ...

D A T A B A S E F I L E S C H A P T E R 7
Other Variables in the Student-Teacher Linkage Files
The linkage files also contain the identification variables required to identify cases and link the
student and teacher files. In addition some tracking and achievement score variables are also
included. The codebooks for Student-Teacher Linkage files contain a complete list of all variables
included.
7.2.5 Missing Codes in the International Data Files
All values assigned to variables in the TIMSS international data files are numeric, and a subset of
the numeric values for each of the variable types is reserved for specific codes related to different
categories of missing data. 9 The missing categories defined below are assigned different values
depending on the field width of the variable and the variable type.
Omitted Response Codes (9, 99, 999, ...)
Omitted response codes are used for questions/items that a student, teacher, or school principal
should have answered but did not answer. These are indicated as "missing" in the codebooks. For
questionnaire data, no differentiation has been made between no answer and invalid answers,
such as checking two or more response options in a categorical question or unreadable or
uninterpretable responses to open-ended questions. In a few cases, data received from a country
in an invalid or inconsistent way were also recoded to "missing.” For cognitive items, an Omitted
Response Code was given only in cases in which the item was left blank; a special code was used
for invalid answers as described below. The specific Omitted Response Code value given
depends on the number of valid codes available for each item.
For Identification, Tracking, or Background Questionnaire Items: An Omitted Response Code
value of 9 is used for categorical items with 7 or less valid response options; for categorical items
with more than 7 categories, a code value of 99 is used. For open-ended background
questionnaire items or other items containing non-categorical values, the omit code is the next
available 9* code greater than the highest response in the defined valid range. Background
questionnaire item values outside the valid ranges were recoded to missing.
For Cognitive Items: An Omitted Response Code value of 9 is used for multiple-choice cognitive
items. For free-response written assessment items and performance assessment items, the twodigit
99 code is used for omitted/blank responses.
Uninterpretable Response Codes (7, 90)
For the cognitive items, separate codes were established to distinguish between totally blank
responses (omitted/missing) and uninterpretable or invalid responses. For multiple-choice items,
cases where more than one response option was checked were classified as uninterpretable and
given a code 7. For the free-response items in the written assessment or the performance
assessment, uninterpretable student responses were given a code 90, which is distinguished from
the code 99 given to items that were left blank.
9
The SAS and SPSS control statement files will recode these missing categories to special numeric missing codes in SAS and
explicit missing codes in SPSS (see Section 7.4).
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