Potential effect modifier | Value | Booster RR* (95% CI) | Wald p value |
Calendar year | 1996–1998 | 0.37 (0.29 to 0.47) | |
1999–2001 | 0.34 (0.23 to 0.51) | ||
2002–2003 | 0.29 (0.21 to 0.41) | ||
2004–2006 | 0.38 (0.29 to 0.51) | 0.64 | |
Model year | 1990–1992 | 0.29 (0.20 to 0.42) | |
1993–1996 | 0.40 (0.30 to 0.53) | ||
1997–2000 | 0.31 (0.23 to 0.41) | ||
2001–2006 | 0.40 (0.30 to 0.55) | 0.33 | |
Motor vehicle type | Car | 0.39 (0.32 to 0.47) | |
SUV | 0.32 (0.23 to 0.44) | ||
Minivan | 0.36 (0.23 to 0.56) | ||
Pickup | 0.16 (0.06 to 0.40) | 0.26 | |
Seating position | Front | 0.22 (0.11 to 0.42) | |
Rear-left | 0.43 (0.35 to 0.54) | ||
Rear-middle | 0.24 (0.16 to 0.37) | ||
Rear-right | 0.35 (0.27 to 0.45) | 0.05 | |
Vehicle rolled over | No | 0.38 (0.32 to 0.46) | |
Yes | 0.28 (0.20 to 0.39) | 0.01 | |
Land use | Urban | 0.38 (0.29 to 0.50) | |
Rural | 0.34 (0.28 to 0.41) | 0.49 | |
Overall | 0.35 (0.30 to 0.41) |
*Risk ratio for children ages 4–8 comparing booster seats (used with seatbelts) vs no restraint and adjusted for age, sex, exposure to air bag deployment, seating position, adult seatbelt use, and all matched collision and vehicle characteristics.