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Police records, held in the Crash Analysis System (CAS) by the New Zealand Transport Agency (NZTA), and hospital admission data held in the Midland Trauma System (MTS) trauma registry, were linked using probabilistic methods. A total of 1,331 casualties resulting from motorcycle crashes on roads in the Midland Region during 2012-2016 were recorded by police. During the same period, and occurring within the same geographical area, a total of 689 on-road motorcycle related crash casualties were admitted to hospital as trauma patients. Linkage of these two datasets revealed substantial under reporting to police of motorcycle crash casualties resulting in hospitalisation. Approximately 56% (386) of hospital trauma admission records could be linked with police CAS records with an additional 303 (44%) patient admission records which could not be linked to any police records. Linkage rates were significantly associated with crash severity as recorded by police, patient injury severity recorded in the trauma registry, patient age, rurality of crash location, and self-presentation to hospital. In particular, younger motorcyclists aged under 45 years were significantly more likely to self-present to hospital with the odds of linkage for self-presenters seventeen times lower than those who did not self-present. The merging of these two datasets has highlighted several sources of bias underlying reporting of motorcycle crashes to police. An understanding of these biases may help to inform policymakers when planning wider preventive strategies designed to reduce the burden of motorcycle crashes in New Zealand.

Police records, held in the Crash Analysis System (CAS) by the New Zealand Transport Agency (NZTA), and hospital admission data held in the Midland Trauma System (MTS) trauma registry, were linked using probabilistic methods. A total of 1,331 casualties resulting from motorcycle crashes on roads in the Midland Region during 2012-2016 were recorded by police. During the same period, and occurring within the same geographical area, a total of 689 on-road motorcycle related crash casualties were admitted to hospital as trauma patients. Linkage of these two datasets revealed substantial under reporting to police of motorcycle crash casualties resulting in hospitalisation. Approximately 56% (386) of hospital trauma admission records could be linked with police CAS records with an additional 303 (44%) patient admission records which could not be linked to any police records. Linkage rates were significantly associated with crash severity as recorded by police, patient injury severity recorded in the trauma registry, patient age, rurality of crash location, and self-presentation to hospital. In particular, younger motorcyclists aged under 45 years were significantly more likely to self-present to hospital with the odds of linkage for self-presenters seventeen times lower than those who did not self-present. The merging of these two datasets has highlighted several sources of bias underlying reporting of motorcycle crashes to police. An understanding of these biases may help to inform policymakers when planning wider preventive strategies designed to reduce the burden of motorcycle crashes in New Zealand.