Figure 4. The item responses of K6.

(A) National RDD sample, (B) national RDD sample of twin pairs, (C) siblings of individuals from the RDD sample, and (D) oversamples from five metropolitan areas in the US. All four subsamples showed that the item response for each of the six items exhibited a common pattern with a boundary between “none of the time” and “a little of the time.” As indicated by the arrow (Fig. 3A), the lines for the six items crossed at a single point between “none of the time” and “a little of the time,” whereas the lines from “a little of the time” to “all of the time” showed a pattern of reduction.