We used the two-sample t-test (for continuous variables with a normal distribution), the Wilcoxon rank-sum test (for continuous variables with a skewed distribution), and the χ2 test to analyze the relation between presence or absence of macular degeneration and potential risk factors. The potential risk factors examined in addition to plasma zeaxanthin, lutein, and lutein plus zeaxanthin were age, sex, body-mass index, pack years smoked, alcohol consumption (including beer and wine intake), serum total cholesterol, history of coronary artery surgery or angioplasty, social class, education, and average spherical equivalent. We used logistic regression to analyze the relation between plasma concentrations of lutein, zeaxanthin, and lutein plus zeaxanthin and risk of macular degeneration, with adjustment for other risk factors. In the multivariate models, we included all risk factors that were associated with the presence or absence of age-related macular degeneration with a significance level of P < 0.10. As lutein and zeaxanthin are lipid-phase nutrients and correlated with serum total cholesterol in these data (r = 0.276 and r = 0.218, respectively), serum total cholesterol was included in the multivariate analyses. Pack years smoked was also included in the multivariate analyses because it has been shown to be a risk factor for age-related macular degeneration in previous studies and was inversely related to plasma zeaxanthin levels in these data (r = −0.109). Odds ratios (OR; with 95% confidence interval [CI]) are shown according to thirds of the distribution of the lutein and zeaxanthin variables. Probabilities are shown for the trend in the odds ratios across the groups.