Table 1.

Characteristics of participants in the study versus the whole population seen

	Study participants (n)	Total population at 18-year follow-up (%)	p Value*
Female gender	52.9% (423/799)	50% (660/1313)	0.196
Active smoking	24.7% (198/799)	28% (368/1313)	0.145
Full-time education	78% (624/799)	68% (898/1313)	<0.001
Atopic at 10†	26.7% (189/709)	26.9% (279/1036)	0.956
Asthma	19.3% (155/799)	17.5% (231/1313)	0.6045

^*Z-test of proportions (two-sided) for comparison between participants analysed in this study and all those assessed at 18 years of age.

^†Numbers reflect those who attended at 10-year and at 18-year follow-up.