A B S T R A C T Objective: Crisis management researchers use the World Assumption Scale (WAS) to demonstrate changes in individuals\\\' assumptions to predict mental health risks based on the Janoff-Bulman model. During the COVID-19 quarantine crisis, adopting preventive behaviors in society required understanding individuals\\\\\\\\\\\\\\\' assumptions about the world, which initially necessitated an examination of the factorial structure of the Assumption World Scale. Therefore, the current research aimed to investigate the psychometric properties of the Assumption World Scale among Iranian students and to examine the relationship between beliefs in a just world, meaningfulness of the world, self-worth, and the adoption or non-adoption of preventive behaviors among students during the COVID-19 quarantine period. Method: Among the Mashhad Ferdowsi University and University of Isfahan, 452 students aged 18 and older (245 women) selected using convenience sampling and responded to the assumption world scale and the preventive behavior adoption questionnaire. The data analyzed using Cronbach\\\\\\\\\\\\\\\'s alpha coefficient, exploratory factor analysis, and stepwise regression analysis. Results: The obtained reliability coefficients were satisfactory. The results of the exploratory factor analysis were relatively satisfactory and corresponded to the main model of the assumption world. Bartlett\\\\\\\\\\\\\\\'s test of sphericity with 496 degrees of freedom at the 0.001 significance level and the KMO test with a value of 0.84 indicated the adequacy of the data for factor analysis. Exploratory factor analysis using principal component analysis with the assumption of eight factors (based on previous research) showed that all 32 questionnaire items obtained coefficients in the range of 0.53 to 0.85 in different factors, and eight factors had eigenvalues greater than one. Moreover, during the quarantine period, students\\\\\\\\\\\\\\\' assumptions about the world significantly correlated with the adoption of preventive behaviors. Stepwise regression showed that non- randomness and the perception of controllability assumptions predicted adopting preventive behaviors. In the first step, when the randomness scale entered the regression equation, its correlation coefficient was 0.44, indicating that 33% of the variance in the adoption of preventive behaviors based on the belief in the non- randomness of world events was explained. In the second step, when randomness and perceived controllability entered the equation together, this percentage increased to 46%. Conclusion: Quarantine and its expansion increase negative effects on mental health. These findings of the COVID-19 quarantine are consistent with previous assumptions about the lack of change in measurement within a sample and suggest an operational solution, aiding in understanding students\\\\\\\\\\\\\\\' assumption worlds in facing trauma and associated cognitive changes in research and practical domains.

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