EQ Health and Wellbeing (EQ-HWB): Assessing the Distinctiveness of Frequency and Severity Response Scales in Measuring Pain and Discomfort

OBJECTIVES: This study aimed was to investigate the distinctiveness and unique contributions of frequency and severity response scales in measuring pain and discomfort within the EQ-HWB instrument across various chronic conditions.

METHODS: A secondary analysis was conducted using data from a cross-sectional survey of 1,008 participants (504 caregivers and 504 care-recipients) administered via Qualtrics between August 2022 and February 2023 in the US. The distinctiveness and performance of the frequency and severity response scales were assessed using correlation analysis, Shannon's indices, Item Response Theory (IRT) and differential item functioning (DIF) using frequency vs severity as an anchor.

RESULTS: Strong correlations (r ≥ 0.5, p < 0.001) were observed among all EQ-HWB pain and discomfort items, with the strongest correlation (r ≥ 0.7, p < 0.001) between pain frequency and severity items across various chronic conditions. Shannon's indices demonstrated higher informativity for frequency scales compared to severity scales across both pain (H’=2.28, J’=0.98 vs H=2.06, J=0.89), and discomfort dimensions (H’=2.18, J=0.94 vs H=2.00, J=0.86). IRT analysis indicated that frequency items were more suitable for differentiating at less intense pain or discomfort, while severity items were more discriminating for identifying higher intensity levels. DIF analysis revealed a systematic difference in responses when responding to pain severity vs frequency (ΔR2 = 0.24, large DIF), but not for discomfort (ΔR2 = 0.001, negligible DIF).

CONCLUSIONS: Frequency scales, particularly for pain, are more informative and discriminatory than severity scales across various chronic conditions. For a longer instrument, including both scales is preferable as pain severity and frequency may provide unique information. However, for a shorter instrument (EQ-HWB-S), the frequency scale may be preferred due to its higher informativity and ability to capture a wider range of pain experiences.