Key statistical concept Although there are clear definitions for all the terms used in this survey, countries might have different methodologies to calculate tonne-kilometer and passenger-kilometers. Methods could be based on traffic or mobility surveys, use very different sampling methods and estimating techniques which could affect the comparability of their statistics. Also, if the definition on road fatalities is very clear and well applied by most coutries, this is not the case for road injuies. Indeed, not only countries might have different definitions but the important underreporting of road injuries in most countries can distort analysis based on these data.
