Table 3

Seasonal effects and inter- and intra-household variation in (natural log transformed) levels of disinfection by-products in tap water (μg/l) from two different data sources

	Seasonal effect† [ (SE)]			Inter-household variation ()	% of total variation‡	Intra-household variation ()	% of total variation‡
	Autumn	Winter	Spring	Inter-household variation ()	% of total variation‡	Intra-household variation ()	% of total variation‡
†Summer: referent category.
‡Estimated total variation:
*p<0.05.
Exposure assessment study (1994–95) (n = 107)
Total trihalomethanes	−0.057 (0.048)	−0.285^*(0.039)	−0.287^* (0.048)	0.041	61	0.027	39
Routine monitoring data (1994–95) (n = 40)
Total trihalomethanes	−0.349*(0.095)	−0.632* (0.095)	−0.332* (0.095)	0.013	22	0.045	78
Routine monitoring data (1991–95) (n = 100)
Total trihalomethanes	−0.511*(0.053)	−0.765* (0.053)	−0.451* (0.053)	0.012	26	0.036	74
Chloroform	−0.557* (0.060)	−0.806* (0.060)	−0.495* (0.060)	0.011	20	0.045	80
Bromodichloromethane	−0.305* (0.060)	−0.635* (0.060)	−0.262* (0.060)	0.016	26	0.045	74
Dibromochloromethane	−0.081 (0.126)	−0.319* (0.126)	−0.050 (0.126)	0.003	2	0.197	98