Background & Aims
Subjective happiness is a psychological factor which may buffer the negative impact of musculoskeletal pain on function. The Subjective Happiness Scale (SHS) is the most commonly used instrument for assessing happiness and has been validated in healthy samples and health conditions such as chronic kidney disease and depression. But, the measurement properties of SHS remains untested in musculoskeletal population. To address this, we sought to evaluate its content validity, internal consistency, test-retest reliability, measurement error, and construct validity in a sample with musculoskeletal pain.
Methods
We first translated and cross-culturally adapted the SHS into Nepali using established guidelines, and then used the Consensus based Standards for the selection of health status Measurement Instruments (COSMIN) recommendations to evaluate the measurement properties of SHS. We recruited 180 individuals with musculoskeletal pain who filled out the SHS and 10 other comparison instruments using either a hard-copy pencil-and-paper form (n = 120) or an online survey (n = 60); repeat assessment was done at 2 weeks time.
The 10 comparison instruments included Patient-Reported Outcomes Measurement Information System (PROMIS®) depression scale, PROMIS® pain intensity, PROMIS® Pain Interference Short Form 6b, PROMIS® Sleep Disturbance Short Form 8b, Pain Catastrophising Scale (PCS), Patient-Specific Functional Scale (PSFS), Connor Davidson Resilience Scale (CDRISC-2), Global Rating of Change (GROC), 2-item Quality of Life (QoL) scale, and Pain Self Efficacy Questionnaire (PSEQ).
Results
The fourth SHS item, which was reverse scored, was found to be problematic during the cognitive debriefing stage and was therefore removed with the approval of the measure developer. Out of score of 21 (which signifies greater happiness), the means scores for the 3-item Nepali SHS in our sample were 15.96 (SD 3.18) and 16.31 (SD 3.14) at initial assessment and the follow-up assessments respectively. We found a single-factor solution for the SHS items, internal consistency of 0.86, and test-retest reliability (ICC) 0.86 (95% CI: .80, .93). Construct validity was also supported with a positive associations with measures of function, resilience, and quality of life and negative associations with depression, pain interference, sleep disturbance and pain catastrophizing.
Conclusions
The Subjective Happiness Scale is a reliable and valid measure for assessing subjective happiness in adults with musculoskeletal pain.
References
Lyubomirsky S, Lepper HS. A measure of subjective happiness: Preliminary reliability and construct validation. Social indicators research 1999;46(2):137-155.
Mokkink LB, Terwee CB, Patrick DL, Alonso J, Stratford PW, Knol DL, Bouter LM, de
Vet HC. COSMIN checklist manual. Amsterdam: University Medical Center 2012.