The present study provides validity and reliability evidence to support the use of the Croatian version of the EHP-5 in everyday monitoring and measuring HRQoL of women with endometriosis. Our findings, although with negligible distinctions, are principally consistent with only three other EHP-5 cross-cultural adaptations and psychometric evaluations published to date [11, 14, 20]. It is important to emphasize that we have demonstrated very good internal consistency and test-retest reliability of both core and modular part of questionnaire. Moreover, our study signifies pain and infertility as the most detrimental factors on overall quality of life among Croatian women with endometriosis.
In order to avoid a risk of spectrum bias, we have included consecutive patients with pathohistologically proven endometriosis. The rationale for not involving asymptomatic controls in this study was to display EHP-5 performance as true as possible. In the French version of EHP-5 psychometric evaluation, Fauconnier and associates have used purposeful sampling design from two different medical centres in order to have better EHP-5 discriminative validity analysis . Although limitations are inevitable in creating the most favourable target population sample, methodological consensus is still lacking .
Another debatable issue is optimal EHP-5 scoring method since there is no precise recommendation from original questionnaire developers . We have adopted evaluation of the dimensional aspect of the EHP-5 separately for the core and the modular part which is consistent to the Turkish and Iranian study [11, 14]. In opposition to separate dimensional aspect evaluation, French EHP-5 version developers have merged all the ratings from core and modular part of questionnaire . A similar scoring method was applied in retrospective study which have estimated impact of laparoscopic treatment of endometriosis on HRQoL . Regardless of implemented scoring method, all abovementioned studies, including ours, have found adequate internal consistency [11, 14, 20].
In terms of internal consistency, our findings are nearly equivalent to Turkish study, showing very good Cronbach's Alpha coefficient of both core and modular part of EHP-5 . This similarity can be explained by comparable initial study setting, inclusion/exclusion criteria and final distribution of disease severity in analyzed sample. Excellent internal consistency (Cronbach α = 0.92) reported by Fauconnier et al. should be interpreted with caution, suggesting that some questionnaire items may be redundant . The evaluation of the core and modular part of questionnaires with 2-week test–retest reliability was performed by Turkish authors using Pearson's product moment correlation coefficient, revealing very good consistence across repeated administration of questionnaire . Their findings are consistent with ours although we have evaluated 2-week test–retest reliability via ICC. Other two published EHP-5 validation studies did not assess test-retest reliability [14, 20].
Our study has demonstrated that pain and infertility had the highest possible negative impact on quality of life for patients with endometriosis which is consistent with findings of Turkish and Iranian authors [11, 14]. However, possible cultural differences and baseline characteristics of sample population determined different responding pattern in French validation study, emphasizing sexual intercourse as one of the most detrimental factors on overall quality of life among patients with endometriosis .
In conclusion, the Croatian version of the EHP-5 was successfully translated, adapted and validated so the questionnaire is now ready for use as a reliable tool for assessing patients with endometriosis in everyday clinical practice. We believe that this validation study will encourage more researches in field of endometriosis preoperative assessment and postoperative surveillance using EHP-5. This short and simple tool will certainly successfully replace current lack of biomedical markers in tracking the progression of endometriosis.