A New Zealand study was aimed at determining if risk factors of cot death differred in the course of the night. A broad national study, comparing 369 cases to 1558 witnesses in New Zealand shows that two third parties of the dead sudden happen at night, between 10 am and 7 hours 30 of the morning. Risk led by ventral position is 3,86 for dead nocturnal and of 7,25 for dead happening in the course of the day; difference is therefore significant.

Risk led by the maternal tobacco is 2,28 for dead nocturnal and of 1,27 for dead diurnal. Dead nocturnal were linked also more strongly to a state of social deprivation. The death of different new-born baby in the daytime and at night, ventral position being more at risk in the daytime, while tobacco and social deprivation are more dangerous at night.