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. 2013 Jun;19(3):153-7.
doi: 10.1136/injuryprev-2012-040345. Epub 2012 Jun 30.

Age, period and cohort effects on the incidence of motorcyclist casualties in traffic crashes

John Langley  1 , Ari Samaranayaka, Dorothy J Begg
Affiliations
Free PMC article

Age, period and cohort effects on the incidence of motorcyclist casualties in traffic crashes

John Langley et al. Inj Prev. 2013 Jun.
Free PMC article

Abstract

Objectives: (1) Estimate age, period and cohort effects for motorcyclist traffic casualties 1979-2008 in New Zealand and (2) forecast the incidence of New Zealand motorcycle traffic casualties for the period 2019-2023 assuming future age, cohort and period effects, and compare these with an estimate based on simple linear extrapolation.

Methods: Age-period-cohort (APC) modelling was used to estimate the individual effects of age, period and cohort after adjusting for the other two factors. Forecasting was produced for three period-effect scenarios.

Results: After adjusting for cohort and period effects, 15-19-year-olds have substantially elevated risk. The period effect reduced in significance over time until the last period, 2004-2008, where the risk was higher than the preceding period. The 10-year cohorts born 1949-1958, 1954-1963, 1959-1968 and 1964-1973, had elevated risk. The forecasting, based on APC modelling, resulted in the lowest estimates of the future incidence being approximately one-third that of the highest estimate (6641).

Conclusion: Trends in motorcycle casualties have been influenced by significant independent age, period and cohort effects. These need to be considered in forecasting future casualties. The selection of the period effect has a significant impact on the estimates. Which period-effect scenario readers choose to accept depends on their views about a wide range of factors which might influence motorcycle use and crash risk over time.

Keywords: MVTC; Motorcycle; adolescent; advocacy; age; behavioural; cohort; forecasting; interventions; legislation; methodology; period; populations/contexts; public health; surveillance; terminology.

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Conflict of interest statement

Competing interests: None.

Figures

Figure 1
Figure 1
Motorcycle casualties (fatal and hospitalised non-fatal): crude and age-adjusted rates by year.
Figure 2
Figure 2
(A) Age effects after adjusting for cohort and period effects. (B) Period effect after adjusting for age and cohort effects. (C) Cohort effect after adjusting for age and period effects.
Figure 3
Figure 3
Indication of model fit: observed versus predicted incidence by year.
See this image and copyright information in PMC

References

    1. International Transport Forum A Record Decade for Road Safety. Paris, 2010
    1. Ministry of Transport Motor Vehicle Crashes in New Zealand 2009. Wellington; Organisation for Economic Co-operation and Development, 2010
    1. Morris C. Motorcycle Trends in the United States. Washington, US Depart of Transportation: Bureau of Transportation Statistics, 2009:6
    1. Ministry of Transport Ministry of Transport Safer Journeys: New Zealand's Road Safety Strategy 2010-2020. Wellington, Ministry of Transport, 2010
    1. Statistics New Zealand National Population Projections: 2004 (base)—2051. Wellington: Hot Off The Press, 2004

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