This study aimed to assess the reliability and validity of Graded Chronic Pain Scale 2.0 (GCPS 2.0) and Jaw Functional Limitation Scale-20 (JFLS-20) of the Malaysian English version of Diagnostic Criteria for Temporomandibular Disorders (M-English DC/TMD). GCPS 2.0 and JFLS-20 underwent psychometric analysis involving content, face, criterion, and construct (exploratory factor analysis (EFA), convergent, discriminant, known group) validity including internal and test-retest reliability on 208 samples. The construct validity was assessed against 14 hypotheses and non-parametric statistics were used to assess the data. The GCPS 2.0 and JFLS-20 had high internal consistencies (α = 0.85 and 0.96) with an intraclass correlation coefficient value of 0.95 and 0.97, respectively. The content validity index for GCPS 2.0 and JFLS-20 were 0.87 and 0.95, respectively. The EFA of GCPS 2.0 identified one factor whereas three factors were identified for JFLS-20. Both instruments had moderate to strong positive correlation with other instruments when assessing for concurrent (r = 0.75-0.80, p < 0.01) and convergent (r = 0.58-0.70, p < 0.01) validity, while moderate to high negative correlation (r = -0.86--0.68, p < 0.01) against the global self-rating oral health items. Based on the study, GCPS 2.0 and JFLS-20 of the M-English DC/TMD proven to be reliable and valid for use in the Malaysian population with TMD.
Keywords: M-English DC/TMD; cross-cultural adaptation; reliability; temporomandibular disorders; validity.