Table 1.

Mental Health Index Outcome Measures Assessed

Index	Trait assessed	Key features
State-Trait Anxiety Index, short form (STAI)	State (S) anxiety—measures the intensity of feelings in the moment, reflective of themes of apprehension, tension, nervousness, worry, and autonomic arousal. Trait (T) anxiety—measures a more stable construct of general feelings of anxiety proneness, such as calmness, confidence, and security, less responsive to change.	A short form, validated in English measure to assess anxiety. Items identifying anxiety are scored on an ascending 1–4 scale, and items without anxiety on a 4–1 scale, with the score summed then multiplied by 20 and divided by 6 to compare it to the state or trait parent form. A score above 39–40 reflects clinically significant state anxiety though this may be 54–55 in geriatric patients. Using item-remainder correlations, the most highly correlated anxiety-present and anxiety-absent items were combined, and correlated with scores obtained using the full form of the STAI. Correlation coefficients greater than 0.90 were obtained using four and six items from the STAI. Acceptable reliability and validity were obtained using six items. The use of this six-item short form produced scores similar to those obtained using the full form. The short form is sensitive to fluctuations in state anxiety. When compared with the full form of the STAI, the six-item version offers a briefer and equally acceptable scale for subjects while maintaining results that are comparable to those obtained using the full form of the STAI.22–25
Patient Health Questionnare-4 (PHQ-4)	Anxiety and depression	A 4-item ultra-short depression/anxiety scale with items drawn from the generalized anxiety disorder-7 and Patient Health Questionnaire-8 scales. This has been validated and shown to have 2 factors, as well as strong concurrent validity with other self-report anxiety/depression scales. Items responses exist as 4-point Likert scales (0–3 range) of duration of a particular symptom, with higher score indicating more persistence of symptoms. There are 2 questions each for anxiety and depression that constitute the respective domains.21
EQ-5D-3L Health Utility Index (EQ-5D-3L)	Health state utility, preference-based quality of life	A well-utilized, well-characterized, and well-validated health utility measure used internationally. This tool used 5 items and 3 levels (“3L”) to measure mobility, self-care, usual activities, pain, and anxiety as well as a Visual Analog Scale (VAS) to measure self-perception of health. From the 5 items, 234 combinations of health states are possible. Each item response includes one of 3 choices, scored 1–3, to create a unique 5-digit score for a person’s health state. The VAS is scored from 0 to 100 as a 2 digit integer, with higher scores indicting better health. Standardized value sets exist to convert scores to a summary index, and exist for multiple countries.26–29, 31 Permissions were obtained from the EuroQoL Research Foundation to use the index in the context of this study.