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Database Analysis 71
Table 4-20. Completeness of contributing factors in TIFA/FARS.
Vehicle Driver Packaging Infrastructure Situational
Configuration Age Package Type Road Surface Pre-Crash Condition
Cargo Body Experience Quantity Shipped Road Condition Event Type
GVW Condition Quantity Lost Road Type Vehicle Speed
Valid License Age (Cargo Tank) Traffic Way Impact Location
Citation Issued Rollover Protection Access Control Primary Reason
Inspection History Speed Limit Accident Type
Design Specification No. of Lanes Weather Condition
Light Condition
Time of Day
Key:
> 95%
50% to 95%
< 50%
Not captured
doned after 2005. The cargo weight variable was known precisely for about 84%, unknown for about
4%, and partially known (light load or full load) for the remaining 12% of the cases.
Generally, the fields derived from the TIFA survey or extracted from FARS are populated fairly
completely. Table 4-20 shows that missing data rates for the fields captured are quite uniformly
low. If the field is present, for the most part, it is complete in more than 95% of the cases. GVW
and quantity shipped are exceptions, because it can be difficult to determine precise values after
the fact, but even for those variables there is some information for 80% to 90% of the cases. Miss-
ing data rates are somewhat higher for vehicle speed prior to the crash, as that is even more diffi-
cult to determine. That information is taken from PAR and is available for about 75% of the cases.
Complete rates of missing data, averaged over five years, are provided for all TIFA variables in
Appendix D (available on the TRB website at www.TRB.org by searching for HMCRP Report 1).
4.4.6 Data Quality
The TIFA system includes multiple layers of quality control. The survey is administered by
means of a telephone interview. Each case record is reviewed by an editor for accuracy, con-
sistency, and completeness. The vehicle identification number of the power unit is decoded,
and the vehicle description from the survey is compared with the original specifications. Infor-
mation about cargo and operations are similarly compared with a library of information that
has been accumulated from over 25 years during which the TIFA survey has been conducted.
Survey information also is compared with the information on the original PAR. Any discrep-
ancies are discussed with the interviewer, who may be required to make additional calls for
information.
Once discrepancies are resolved, the data are then entered with verification. At that point,
there is a computerized check of each batch of keypunched cases for consistency and to identify
any invalid codes or responses that are outside of the usual range. Unusual responses are
reviewed by the data editors. Finally, when a data year is complete, there is a computerized check
of all cases for invalid codes, inconsistent data, or unusual responses.
4.4.7 Additional Fields
Although the TIFA survey adds valuable detail to the FARS data, additional data fields could
add important detail about hazmat packaging and also enhance the information available on
