The equations were reanalyzed after adding the BDI to the
model. A small number of missing values were replaced by the
mean of the variable. In order to identify possible multicollinearity,
tolerance and the variance inflation factor (VIF) were calculated.
In order to study the effect of pain on the association, an
interaction term was added to the equation. The pain severity level
was considered as a moderator. The interaction was tested for
those HA scales that had shown association with pain-related
anxiety in the previous equations. The interaction term (pain
severity6HA scale) was added after controlling the main effects of
pain severity and the HA scale in question. The nature of
interaction was studied visually by drawing regression lines
representing the regression curves at +1SD, mean and 21 SD
values of the pain variable [