Table 1

Variables measured by each of the four study methods (collection methods in parentheses)

Variables	Observational survey (observation)	Interview/inspection (observation/ inspection/self report)	Self administered questionnaire (self report)	Focus group (self report)
Drivers
Sex	Estimate	Yes	Yes	Yes
Age	Estimate	Yes	Yes	Yes
Ethnicity	No	Yes	Yes	Yes
Education	No	Yes	Yes	Yes
Household income	No	Yes	Yes	Yes
Seat belt use	Yes	Yes	No	No
Relationship to child(ren)	No	Yes	Yes	Yes
Vehicles
Type	Yes	Yes	Yes	No
Make	Yes	Yes	Yes	No
Where manufactured	No	Yes	No	No
Children
Age	Estimate	Yes	No	No
Sex	Estimate	Yes	No	No
Number in household	No	No	Yes	No
CRD use
Position in car	Yes	Yes	No	No
Type	Yes	Yes	No	No
Ownership	No	Yes	Yes	Yes
Frequency of removal	No	Yes	Yes	Yes
Ease of use	No	Yes	Yes	Yes
Fitting in vehicle examined	No	Yes	No	No
Placement of child examined	No	Yes	No	No
Reasons for non use	No	Yes	Yes	Extensive
Barriers to use	No	Limited	Limited	Extensive
Potential to give rate of use of CRD	Yes	Yes	No	No