Table 2: Linear model of radon levels based on estimates of home metrics effect and descriptive statistics based on sum of squares type III general linear model where year of construction is controlled for*

Variable	df	Sum of square	Mean square	F	p value
Corrected model	150	120.519‡	0.803	2.226	0.000
Intercept	1	6.857	6.857	19.001	0.000
Year of construction†	1	18.433	18.433	51.080	0.000
Found	3	2.150	0.717	1.986	0.114
Build	3	0.775	0.258	0.716	0.542
Floor	4	2.166	0.541	1.500	0.200
Room	2	1.996	0.998	2.765	0.063
Area	4	2.593	0.648	1.797	0.127
Found × build	2	1.776	0.888	2.461	0.086
Found × floor	9	3.891	0.432	1.198	0.292
Found × room	3	0.066	0.022	0.061	0.980
Found × area	11	3.992	0.363	1.006	0.439
Build × floor	7	3.288	0.470	1.302	0.246
Build × room	5	1.054	0.211	0.584	0.712
Build × area	10	6.634	0.663	1.838	0.050
Floor × room	7	5.929	0.847	2.347	0.022
Floor × area	16	5.395	0.337	0.934	0.529
Room × area	8	5.514	0.689	1.910	0.055
Found × build × floor	0	0.000	-	-	-
Found × build × room	0	0.000	-	-	-
Found × build × area	0	0.000	-	-	-
Found × floor × room	2	1.927	0.964	2.670	0.070
Found × floor × area	11	2.707	0.246	0.682	0.757
Found × room × area	2	0.855	0.427	1.184	0.306
Build × floor × room	1	0.124	0.124	0.343	0.558
Build × floor × area	10	4.935	0.494	1.368	0.190
Build × room × area	6	4.581	0.764	2.116	0.049
Floor × room × area	12	3.283	0.274	0.758	0.694
Found × build × floor × room	0	0.000	-	-	-
Found × build × floor × area	0	0.000	-	-	-
Found × build × room × area	0	0.000	-	-	-
Found × floor × room × area	0	0.000	-	-	-
Build × floor × room × area	1	0.074	0.074	0.206	0.650
Found × build × floor × room × area	0	0.000	-	-	-
Error	1332	480.679	0.361
Total	1483	31 569.683
Corrected total	1482	601.199

Note: build = build type, df = degrees of freedom, floor = floor tested, found = foundation type, room = room tested.

*Dependent variable ln(radon concentration).

†Covariate.

‡R² = 0.20, adjusted R² = 0.11.