Venous thrombosis risk for quartiles of fibrinogen γ′ and quartiles of total fibrinogen. Values are measured in units per deciliter. For each of the 16 strata, the odds ratios were calculated. Because only 2 patients, but no controls, were present in the most logical reference category with fibrinogen γ′ 132 or greater and total fibrinogen less than 101, the stratum with fibrinogen γ′ less than 86 and total fibrinogen less than 101, which contained 68 patients and 69 controls, was set as the reference category (OR, 1) (marked by an asterisk in the figure).