TABLE 3.

Fraction of biomarker intake variation explained by linear regression of log-biomarker intake on log(FFQ) or log(FFQ+Supp) intake and covariates in an NPAAS Nutritional Biomarker Study (n = 436) and in a Measurement Precision subcohort (n = 5488)¹

Nutritional variable	CVD (n = 436)	Covariates (n = 5488)	Cancer (n = 436)	Covariates (n = 5488)	Diabetes (n = 436)	Covariates (n = 5488)
α-Carotene	0.401	0.255	0.384	0.250	0.388	0.249
β-Carotene	0.606	0.509	0.682	0.618	0.587	0.499
Lutein + zeaxanthin	0.573	0.521	0.546	0.516	0.563	0.516
α-Tocopherol	0.762	0.669	0.662	0.604	0.673	0.614

¹Listed numbers are the fraction of log-biomarker intake explained (R²) by log(FFQ) intake and covariates for α-carotene and lutein + zeaxanthin, and by log(FFQ+Supp) and covariates for β-carotene and α-tocopherol. Covariates considered for inclusion in regression models for CVD, cancer, and diabetes analyses are listed in Supplemental Table 1. Covariates are included through forward selection with a P value threshold of 0.1, and at each step are retained using the same criterion. CVD, cardiovascular disease; FFQ+Supp, food-frequency questionnaire plus dietary supplement; NPAAS, Nutrition and Physical Activity Assessment Study; R², % of variation in response variable explained by regression variable(s).