The International Grief Questionnaire (IGQ): A new measure of ICD-11 Prolonged Grief Disorder.

Prolonged grief disorder (PGD) is included in the 11th version of the International Statistical Classification of Diseases and Related Health Problems (ICD-11). This study sought to test the validity and reliability of a new brief measure to screen for ICD-11 PGD—the International Grief Questionnaire (IGQ). The psychometric properties of the IGQ were tested using data collected from two bereaved samples of adults from the United Kingdom (n = 1,012) and Ireland (n = 1,011). Confirmatory factor analysis demonstrated that a correlated two-factor model best captured the latent dimensionality of the IGQ in both samples. Estimates of internal reliability were high, whereas the convergent and concurrent validity of the scale were supported through strong associations with external measures. Measurement invariance and differential item functioning testing showed no statistically significant difference in the latent structure of the IGQ nor the functioning of the IGQ items by age, sex, and nationality. For participants who were bereaved for more than 6 months, the rates of probable PGD derived from the IGQ were 10.9% and 15.3% for the Irish and U.K. samples, respectively. The IGQ is a brief, easy-to-use, self-report screening measure that captures all diagnostic criteria of PGD set forth in the ICD-11. Findings from this study provide initial support for the validity, measurement invariance, and reliability of the IGQ among two national samples.