Evaluation of the
Edinburgh Post Natal Depression Scale using Rasch analysis
Background The
Edinburgh Postnatal Depression Scale (EPDS) is a 10 item self-rating post-natal
depression scale which has seen widespread use in epidemiological and clinical
studies. Concern has been raised over the validity of the EPDS as a single
summed scale, with suggestions that it measures two separate aspects, one of
depressive feelings, the other of anxiety. Methods As part of a larger
cross-sectional study conducted in Results Rasch analysis of the
data from the ten item scale initially demonstrated a lack of fit to the model
with a significant Item-Trait Interaction total chi-square (chi Square=82.8, df
=40; p<.001). Removal of two items (items 7 and 8) resulted in a
non-significant Item-Trait Interaction total chi-square with a residual mean
value for items of -0.467 with a standard deviation of 0.850, showing fit to
the model. No DIF existed in the final 8-item scale (EPDS-8) and all items
showed fit to model expectations. Principal Components Analysis of the
residuals supported the local independence assumption, and unidimensionality of
the revised EPDS-8 scale. Revised cut points were identified for EPDS-8 to
maintain the case identification of the original scale. Conclusions The results of this study
suggest that EPDS, in its original 10 item form, is not a viable scale for the
unidimensional measurement of depression. Rasch analysis suggests that a
revised eight item version (EPDS-8) would provide a more psychometrically
robust scale. The revised cut points of 7/8 and 9/10 for the EPDS-8 show high
levels of agreement with the original case identification for the EPDS-10. |
Title: Evaluation of the Edinburgh Post Natal Depression Scale using Rasch analysis