ON 1 JUNE 1972, THE WEARING OF AVAILABLE SEATBELTS BY FRONT SEAT OCCUPANTS (DRIVERS AND FRONT SEAT PASSENGERS) BECAME COMPULSORY IN NEW ZEALAND. A COMPARISON OF FATALITY RATES FOR FRONT SEAT OCCUPANTS DURING THE TWO YEARS PRECEDING AND FOLLOWING THE LAW HAS BEEN MADE BY TOOMATH AND LAURENSON (1976). THE FATALITY RATE PER MILLION GALLONS OF TAXABLE PETROL CONSUMPTION SHOWS A DROP OF ABOUT 7% FOR SUCH OCCUPANTS, ACCOMPANIED BY A SURVEYED USAGE RATE INCREASE FROM 25% TO 67%. CONSIDERING THE WELL ESTABLISHED VALUE OF SEATBELTS IN REDUCING ROAD TRAUMA, THE SIZE OF THE FATALITY REDUCTION IS RATHER DISAPPOINTING. FOR CLARIFICATION, FATALITY RATES CRUDELY ADJUSTED FOR EXPOSURE WERE SEPARATELY CALCULATED FOR BELTED AND UNBELTED FRONT SEAT OCCUPANTS. COMPARATIVE RATES BEFORE AND AFTER THE LAW WERE SOMEWHAT SURPRISING, SO A MODEL WAS CONSTRUCTED IN WHICH THE AFTER-LAW USE RATE COULD BE TREATED AS AN UNKNOWN. PRINCIPAL FINDINGS WERE: BASED ON SURVEYED USE DATA, THE FATALITY RATE FOR BELTED FRONT SEAT OCCUPANTS INCREASED AFTER THE LAW; LIKEWISE SO DID THE FATALITY RATE FOR UNBELTED FRONT SEAT OCCUPANTS. SINCE THE FATALITY RATE FOR ALL FRONT SEAT OCCUPANTS (AGGREGATE OF BELTED AND UNBELTED) DECREASED, THERE IS AN APPARENT PARADOX THAT CAN BE RESOLVED BY ASSUMING A QUALITATIVE SHIFT IN THE USER POPULATION. INFERENTIAL ANALYSIS SUGGESTS THAT BELT USE REDUCED THE PROBABILITY OF FATAL INJURY, IN A GIVEN CRASH, BY ABOUT 40%. SIMILAR ANALYSIS SUGGESTS THAT THE EFFECTS OF THE LAW, WHEN ADDED TO THOSE OF VOLUNTARY USE, WERE TO SAVE ONLY ABOUT 40% AS MANY LIVES AS COULD HAVE BEEN SAVED BY UNIVERSAL BELT USAGE AMONG FRONT SEAT OCCUPANTS. APPARENTLY THOSE STILL UNBELTED AFTER THE LAW REPRESENT A PARTICULARLY HIGH-RISK GROUP, BY WHOM INCREASED BELT USE WOULD RESULT IN DISPROPORTIONATE SAVINGS.(Author/publisher).
Abstract