The English version of the four-dimensional symptom questionnaire (4DSQ) measures the same as the original Dutch questionnaire: a validation study.
BACKGROUND
Translations of questionnaires need to be carefully validated to assure that the translation measures the same construct(s) as the original questionnaire. The four-dimensional symptom questionnaire (4DSQ) is a Dutch self-report questionnaire measuring distress, depression, anxiety and somatization.


OBJECTIVE
To evaluate the equivalence of the English version of the 4DSQ.


METHODS
4DSQ data of English and Dutch speaking general practice attendees were analysed and compared. The English speaking group consisted of 205 attendees, aged 18-64 years, in general practice, in Canada whereas the Dutch group consisted of 302 general practice attendees in the Netherlands. Differential item functioning (DIF) analysis was conducted using the Mantel-Haenszel method and ordinal logistic regression. Differential test functioning (DTF; i.e., the scale impact of DIF) was evaluated using linear regression analysis.


RESULTS
DIF was detected in 2/16 distress items, 2/6 depression items, 2/12 anxiety items, and 1/16 somatization items. With respect to mean scale scores, the impact of DIF on the scale level was negligible for all scales. On the anxiety scale DIF caused the English speaking patients with moderate to severe anxiety to score about one point lower than Dutch patients with the same anxiety level.


CONCLUSIONS
The English 4DSQ measures the same constructs like the original Dutch 4DSQ. The distress, depression and somatization scales can employ the same cut-off points as the corresponding Dutch scales. However, cut-off points of the English 4DSQ anxiety scale should be lowered by one point to retain the same meaning as the Dutch anxiety cut-off points.
Department of General Practice and Elderly Care Medicine & EMGO Institute for Health and Care Research, VU University Medical Centre , Amsterdam , the Netherlands.
Berend
B
Terluin
Niels
N
Smits
Baukje
B
Miedema
D000293:Adolescent; D000328:Adult; D003431:Cross-Cultural Comparison; D005194:Family Practice / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D001523:Mental Disorders / Q000175:diagnosis*; D008875:Middle Aged; D009426:Netherlands; D011594:Psychometrics / Q000379:methods*; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires / Q000592:standards*; D014175:Translating; D055815:Young Adult