Testing Previously Proposed Models of the Tonic Immobility Scale in a Peritraumatic Sample of Israeli Civilians: Support for a Three-Factor Model

Objective: Tonic immobility (TI) is a peritraumatic response to extreme threats. It is associated with trauma psychopathology and poor treatment outcomes. Yet, previous psychometric evaluations have yielded inconsistent results regarding the number of latent factors of the Tonic Immobility Scale (TIS). Moreover, the TIS has never been validated in a Hebrew-speaking population. This study had two objectives: (a) to reassess previously proposed models of the TIS to determine whether it is best represented by a one-factor model of TI, a two-factor model of TI and fear, or a three-factor model of TI, fear, and detachment; and (b) to validate the TIS in a Hebrew translation. Method: A sample of Israeli adults was culled from an online survey following rocket attacks. Confirmatory factor analysis was applied to test the previously proposed models, and Pearson’s correlations were used to test the association between each of the subscales representing the latent factors and psychological distress. Results: The best representation of the datawas provided by a threefactor model with latent constructs of TI, fear, and detachment. All three peritraumatic responses had significant correlations with peritraumatic distress. Moreover, the internal consistency of the TIS was good for the three subscales; this supports the reliability of the Hebrew version. Conclusion: This study supports using a three-factor model with latent constructs, and the scale appears to be psychometrically sound when translated into Hebrew. Future research should seek to replicate these findings in different trauma populations and should study the unique association of trauma symptomatology.