Observed % 84.00 Low risk categories: Almost entirely fat: 0-25% Scattered fibroglandular densities: > 25-50% High risk categories: Heterogeneously dense: > 50-75% Extremely dense: > 75% Expected % 33.04 Garrido-Estepa et al. BMC Cancer 2010, 10:485 http://www.biomedcentral.com/1471-2407/10/485 Page 4 of 8 Table 3 Agreement between the first and second measures using the BI-RADS classification Number of mammograms classified in each category in the first and second measurements Second measure First measure Almost entirely Scattered fibroglandular Heterogeneously dense Extremely dense fat densities Almost entirely fat 147 13 0 0 Scattered fibroglandular 14 101 10 0 densities Heterogeneously dense 0 14 48 6 Extremely dense 0 0 3 19 Total 161 128 61 25 Kappa-statistic estimation Agreement Kappa (95% CI) Weighted Kappa (95% Kappa high/low risk (95% CI) CI) Total 160 125 68 22 375 0.761 (0.706-0.814) 0.904 (0.877-0.928) 0.815 (0.746-0.885) between the pattern-based classification of the Wolfe, Tabár scales and semi-quantitative scales, BI-RADS and Boyd, was studied graphically to observe how their respective categories expressed density percentages. Confidence intervals were calculated. Bootstrapping methods were used when more than two categories or weighted kappa were involved; to optimize the results, bootstrapping was performed with 5000 replications. In high/low-risk categorization, confidence intervals for the kappa statistic were calculated using a previously described analytical method [13]. All statistical analyses were performed using the Stata version 10 computer software program. Table 4 Agreement between the first and second measures using the Boyd classification Number of mammograms classified in each category in the first and second measurements Second measure First measure A B C D E F Total A = 0% 6 4 0 0 0 0 10 B = > 0-10*% 4 56 11 0 0 0 71 C = 10-25*% 0 16 50 13 0 0 79 D = 25-50*% 0 0 14 102 9 0 125 E = 50-75*% 0 0 0 14 48 6 68 F = ≥75% 0 0 0 0 3 19 22 Total 10 76 75 129 60 25 375 Kappa-statistic estimation Agreement Kappa (95% CI) Weighted Kappa (95% CI) Kappa high/low risk (95% CI) Observed % Expected % 74.93 22.88 0.675 (0.616-0.733) 0.917 (0.898-0.933) 0.822 (0.754-0.891) Low risk categories: A: 0% B: > 0-10*% C: 10-25*% D: 25-50*% High risk categories: E: 50-75*% F: ≥75% *Upper bound excluded