Table 1: Characteristics for participants.

First yearSecond yearThird yearFourth yearFifth year

Total students10711310012399
Refusal5765242315
Participants50487610084
Missing value records47867
Finally included records4641689477
Included records
 Age, years (M ± SD)21.1 ± 1.3923.4 ± 4.7623.0 ± 1.9724.8 ± 3.4825.4 ± 4.08
 Male2525386349
 Female2116303128
 Response rate 43.0%36.3%68%76.4%77.8%

M: mean.
SD: standard deviation.