The Central Statistical Office warns that the occasional occurrence of major disasters can cause year to year fluctuations, so care should be taken when comparing figures year by year. For example, the 1983 to 1993 average for water transport is heavily influenced by the accidents involving the ‘Herald of Free Enterprise (193 deaths) in 1987 and the 'Marchioness’ (51 deans) in 1989.They are good examples of how single events can distort statistics.