Fig. 1

Conceptual relationship of the four items comprising the CDC Healthy Days Measures core module (HRQOL-4). Q1 captures respondents’ overall assessment of their health in the recent past, incorporating both their physical and psychological health, with some consideration for the more distant past and future. Q2 and Q3 measure physical and mental health in the past 30 days, respectively, conceptualized as independent domains. Q4 captures perceived disability or poor functional status as a result of the poor mental or physical health days measured in Q2 and Q3. Adapted with permission from Hennessy CH, et al. Public Health Rep. 1994;109(5):665–72