Structural Validity of the Tonic Immobility Scale in a Population Exposed to Trauma: Evidence from Two Large Brazilian Samples

Tonic Immobility is a temporary state of motor inhibition in situations involving extreme fear. The first scale developed for its assessment was the 10-item Tonic Immobility Scale (TIS). However, there are still few studies on its structural (dimensional) validity. The objective of this study was to reassess the factor structure of the TIS applied to representative samples exposed to general trauma of two Brazilian mega-cities. The sample comprised 3,223 participants reporting at least one traumatic experience. In São Paulo (n = 2,148), a Confirmatory Factor Analysis (CFA) first tested the originally proposed two-dimensional structure. This was followed by sequential Exploratory Structural Equation Models to identify the best fitting model, and subsequently tested in Rio de Janeiro (n = 1,075) via CFA. Alternative reduced versions were further explored using the aggregate sample. Model-based Item Response Theory location parameters were also investigated.

An absence of factor-based convergent and discriminant validity rejected the original proposition. However, the one-dimensional structure still held several residual correlations. Further exploration indicated the sustainability of reduced versions with seven (alternative A) and six (alternative B) items. Both presented excellent fit and no relevant residual item correlation. According to the IRT location parameters, items in alternative B covered a wider range of the latent trait. The Loevinger’s H scalability coefficients underscored this pattern. The original model did not hold. A one-factor solution was the most tenable in both large samples, but with significant item residual correlations, indicating that content redundancies persisted. Further reduced and simplified versions of the TIS proved promising. Although studies are yet to be carried out in other settings, it is the authors’ impression that the restricted versions of the TIS are already apt for use in epidemiologic studies since the pros tend to outweigh the cons.

Michael Reichenheim is an Associate Professor at the Institute of Social Medicine, State University of Rio de Janeiro and Deputy Head (Director) of the IMS from 2008 to 2016. He has been a member of the editorial boards of two scientific journals, Journal of Public Health and Paediatric and Perinatal Epidemiology for over a decade. Michael graduated in Medicine (Pediatrics) from the Federal University of Rio de Janeiro in 1979; obtained his MSc degree in Maternal and Child Health at the Institute of Child Health, University of London in 1984; and finished his PhD in Public Health in 1988. His interests have also focused on methodological issues, especially regarding the assessment of epidemiological measurement tools/instruments (including models for cross cultural adaptation processes, software development and teaching materials)

Tuesday, November 28, 2017 - 2:00pm
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