The Pain-Related Fear Scale: The validation of an instrument to measure pain-related fear in younger adults under 45 years of age with obesity.

Background: The existence of pain-related fear appears to present an obstacle for health promoting behaviour change, particularly among younger adults with obesity. Measures developed and validated for middle-and-older age groups lack validity in younger adults under 45 years of age. This paper reports on the development and psychometric properties of a new instrument, based on a conceptual framework, to measure pain-related fear in younger adults. Methods: A cross sectional survey design was employed. 236 participants aged 18 to 45 years were recruited to participate. Participants completed three existing pain-related fear instruments mapped to a conceptual framework. Exploratory and confirmatory factor analysis identified the dimensions of the new Pain-Related Fear Scale. Construct validity was assessed by comparing scores between physical activity groups; criterion validity by correlation with the Tampa Scale of Kinesiophobia and reliability by Cronbach’s alpha. Differences in scores in the Pain-Related Fear Scale were explored across BMI subgroups. Results: A four-factor model with 12 items met the most acceptability thresholds for a good fitting model (CFI = 0.983; GFI = 0.953; RMSEA = 0.046; SRMR = 0.0301). Higher mean scores on the Pain-Related Fear Scale were seen among those reporting low activity compared to high activity levels (F= 4.684; P= 0.01). Modest correlation was observed between the new instrument and Tampa Scale of Kinesiophobia (r= 0.508;95% CI= 0.389-0.612). Cronbach’s alpha was 0.842. Scores were higher in the obese subgroup compared to the healthy bodyweight group (mean difference= -7.42; CI= -12.26 - -2.58; P= 0.001). Conclusion: The Pain-Related Fear Scale is a psychometrically valid measurement of pain-related fear for adults with obesity aged between 18 to 45 years. The instrument can support research relating to barriers to physical activity, and potentially has clinical utility as a screening and outcome measurement.