Abstract

Objective: Since its first definition, the number of dimensions of the posttraumatic stress disorder (PTSD) has increased (e.g., 1 to 7). This could be caused by 2 methodological reasons. First, the studies do not select representative samples of the population and do not consider the magnitude of exposure to the same event. Second, they use nonrobust data analysis, which increases the number of dimensions artificially. The aim is to determine how many dimensions PTSD has, when both sources of error are controlled. Method: From 25,400 representative participants of the same population exposed to an earthquake and evaluated with the Davidson Trauma Scale, 127 smaller samples of 200 participants were obtained and classified according to the Mercalli magnitude. Parallel factor analyses (PFA), exploratory structural equations models (ESEM), and classic exploratory factor analysis (EFA) were applied to each sample. Results: There were significant differences in fit and number of dimensions between the high and low Mercalli magnitude. In high exposure conditions: There were 1 dimension according to PFA and 3 according to EFA; ESEM and CFA indicated good fit. The main finding was that PTSD has a unique dimension that includes all of its symptoms. Conclusions: The need to use robust methods of analysis to evaluate data from samples homogeneously exposed to the same potentially traumatic event is argued.