Fig. 2

Person-item threshold distribution in community-dwelling adults in the US. The horizontal logit ruler represents both item difficulty and person ability. The pink histograms show the frequencies of the person's ability level in terms of positive mental well-being. A higher logit value indicates the person has a higher level of positive mental well-being. The blue histograms represent the frequencies of item difficulty level, and the items are organized from the easiest on the left to the hardest on the right. The green curve is showing the test information function, displaying where most information about the persons is provided and are inverse functions of the measurement standard errors (SE)