Letter to the Editor in response to "Course and predictors of posttraumatic stress-related symptoms among family members of deceased ICU patients during the first year of bereavement"

A more advanced model of prediction of severe PTSD symptoms for bereaved family members of ICU decedents was suggested by examining interactions and multicollinearity among the proposed independent variables, selecting variables through stepwise regression, and evaluating external validity of our final model. Without a well-established theory [3] or conceptual model guided by the existing studies for factors associated with ICU bereaved family members’ severe PTSD symptoms, interactions among variables to identify moderation effects of specific variables (which increase the chance of multicollinearity [4]—a concern also raised in the letter) were not examined in our model. By the same token, instead of stepwise regression, we used simultaneous regression model—an automatic procedure for statistical model selection when there is a large number of potential explanatory variables and no underlying logical or theoretical basis on which to set the criteria for the variable selection [5].