Structural validity of the Brazilian version of the Sense of Coherence scale (SOC-13) in oral health research: exploratory and confirmatory factor analysis

BACKGROUND: The Sense of Coherence (SOC) construct has been used worldwide in oral health research, but rigorous factor analyses of the scale are scarce. We aim to test the dimensional structure of the Brazilian short version of the SOC scale with 13 items. METHODS: This study is a secondary analysis of four independent cross-sectional Brazilian studies on oral health, using the 13-items SOC scale. Sample 1 was conducted on 1760 mothers and 1771 adolescents. Sample 2 comprised 1100 adults. Sample 3 had 720 adults and older individuals. Sample 4 comprised 664 adolescent students. Confirmatory Factor Analysis (CFA) was conducted on sample 1 to compare two models: 3-factor versus 1-factor. Because they were refuted, Exploratory Factor Analysis was implemented in samples 2 and 3. Modified models were tested in sample 4 using CFA. All analyses were conducted with MPlus version 7.11. RESULTS: CFA of sample 1 resulted in an unacceptable fit (RMSEA = 0.12;CFI = 0.78; TLI = 0.73; and WRMR = 3.28) for 1-factor model and 3-factor (RMSEA = 0.10; CFI = 0.87; TLI = 0.84; and WRMR = 2.50). The EFA on samples 2 and 3 showed, respectively, two eigenvalues greater than 1 (4.11 and 1.56) and (4.32 and 1.42), but the scale items soc1, soc2 and soc3 formed an uninterpretable second factor. Another CFA, using sample 4, showed acceptable model fit after removing those three items and also soc11 (RMSEA = 0.05; CFI = 0.98; TLI = 0.99; and WRMR = 0.71). CONCLUSION: The results indicate that the SOC-13 scale needs further adjustments. The one-factor model with nine items showed a good statistical fit, but the implications of excluding items should be further investigated, considering the scale's content validity, cross-cultural adaptation and theoretical background.