Table 4.

Percent change in concentrations of major PCBs associated with a unit increase in each of the fixed effects included in the mixed-effects model (Model 2a).

Explanatory variables	PCB Congener
	28	52	101	105	118	138	153	180
Residential construction dateb	−9*	−9*	−15*	−18*	−17*	−14*	−15*	−15*
Mother’s agec	18*	14*	13	11	12	7	11	12
Residential square footaged	−5	−6	−11*	−11*	−11*	−8	−10*	−9
Vacuum has disposable bag	4	8	24*	36*	39*	19	25*	33*
Time between rounds (reference)e	−4*	−3	−3	−0.4	−3	−12*	−1	−6*
Time between rounds (cases)e	−0.4	−4	−4	−6*	−4	−3	−3	−1
Time between rounds (construction)e	3	4*	5*	5	6*	7*	4	6*
Time between rounds (floors)e	−5*	−3	−6*	−6*	−6*	−6*	−7*	−4

^*Regression coefficient for fixed effect in Model 2 is significantly different from 0, p-value<0.05.

^aIn this table, Model 2 was fit for 448 observations including 403 samples collected from 202 homes during repeat sample collections and 45 duplicate samples; excluding 139 observations without covariate data (40 inter-batch quality control replicates and 87 samples with 10 duplicates from homes that were sampled during Round 1 only).

^bPercent change per 10 year increment in residential construction date

^cPercent change per 5 years increment in mother's age

^dPercent change per 500-sf increment in residential square footage

^ePercent change per 1 year increment in time between rounds