Relationship between sleep pattern, nocturnal cellular phone usage and the bullying status*.

*The number of the participants and percentage (in brackets) are described in each column, except for nocturnal sleep duration and school size, in whose column mean and SD (in brackets) are described instead. The numbers of missing data for each variable are 511 for sleeping hours, 45 for irregular bedtime, 157 for having a mobile phone, and 184 for e-mail or calling after bedtime. The odds ratios compared to the uninvolved subjects were calculated by logistic regression analysis adjusted for sex, age, survey area, the number of parents living together, drinking alcohol, usage of recreational drugs, and domestic violence from adults (forced entry).**E-mail exchange or calling after lights-off (everyday)¶; p