{"paper_id":"e9f51076-521c-40ae-9f1a-668971ede004","body_text":"Chronic diseases such as endometriosis can affect health-related quality of life (HRQoL). 1  HRQoL is a multidimensional concept that refers to the patient’s general\nperception of the effect of her disease and treatment on physical, psychological,\nand social aspects of daily life. 2 –  4  HRQoL is commonly assessed as a\npatient-reported outcome, that is, a clinical outcome reported directly by the\npatient. 3 , 5 \nA patient-reported outcome measure (PROM) of HRQoL can be generic, applicable to\npatients with a variety of conditions, or disease-specific. 6  Disease-specific instruments may detect change in important aspects of\ncertain conditions not accessible by generic instruments. 7  The Endometriosis Health Profile-30 (EHP-30) is a disease-specific PROM of\nHRQoL consisting of a core and modular questionnaire. 8 , 9  The original English version was\ndeveloped in the United Kingdom and first presented in 2001. 8  The items, or questions, were generated from in-depth interviews of 25\npatients with endometriosis visiting a gynecology clinic at a large tertiary\nreferral hospital in Oxford. 8\nThe EHP-30 is available in many languages. Evaluation of measurement properties, that\nis, reliability, validity, and responsiveness, has been performed for several of\nthese, however primarily for the core questionnaire. 10 – 15  With multinational and\nmulticultural studies increasing, adequate translation, cross-cultural adaptation,\nand cross-cultural validation are essential to ensure equivalence of a PROM in\nlanguages and cultures other than the original. 16  The Consensus-based Standards for the selection of health Measurement\nINstruments (COSMIN) group has developed user-friendly and easily applicable\nchecklists to evaluate the methodological quality of primary studies on measurement properties. 17  According to these checklists, few, if any, of the EHP-30 validation studies\nhave included adequate sample sizes for test–retest reliability analysis. 18  Test–retest reliability is an important aspect of reliability, ensuring that\nchanges detected by an instrument are not random. 3  However, analysis depends on patients being in stable condition. Although\nendometriosis is sometimes characterized by disease fluctuation, it is also thought\nto be stable for longer periods of time. Fewer may be in stable condition among\npatients attending secondary and tertiary referral centers compared with members of\npatient registries and patient associations.\nThe aim of this study was to evaluate the measurement properties of the Norwegian\nversion EHP-30 (NO-EHP-30) and thereby its suitability for future use in\nendometriosis research in Norway or as part of multinational studies.\n\nWomen with endometriosis were recruited from the Norwegian Endometriosis\nAssociation. Inclusion criteria were 18–45 years of age and surgically confirmed\ndiagnosis. Cross-sectional data collection was performed from 2012 to 2013. A\nset of two anonymous postal questionnaires was sent to potential participants.\nEach questionnaire included questions on background information, NO-EHP-30, and\nShort form-36 version 2 (SF-36v2). 19  Participants were asked to fill in the second questionnaire 1 month after\ncompleting the first questionnaire, for test–retest reliability analysis. A\nperiod of 1 month between the test and retest was chosen to minimize memory\neffects. A period of 1 month was also thought to increase the chances of the\nrespondents being in the same phase of their menstrual cycle, which in turn may\nbe relevant regarding endometriosis complaints and reporting of HRQoL.\nBackground information included age, height, and weight. Diagnostic delay was\nrecorded as year receiving diagnosis minus year the participant started having\nsymptoms. Furthermore, a multiple choice question on organs/anatomic locations\naffected by endometriosis and two open questions inviting free description of\nprevious and present treatment were included. Finally, the participants were\nasked whether they had experienced dysmenorrhea, pelvic pain, dysuria, and/or\ndyschezia during the 4 weeks prior to answering the questionnaire.\nThe responses are based on patient experiences during the 4 weeks prior to\nanswering the questionnaire. The core questionnaire is composed of 30 items\ngrouped into five scales: pain (11 items), control & powerlessness (6\nitems), emotional well-being (6 items), social support (4 items), and self-image\n(3 items). The modular questionnaire is composed of 23 items grouped into 6\nscales: work life (5 items), relationship with children (2 items), sexual\nintercourse (5 items), medical profession (4 items), treatment (3 items), and\ninfertility (4 items). The modular questionnaire is characterized by the\npossibility of responding only to scales which the patient deems relevant to\nher. All scales can achieve a minimum score of 0, indicating low disability, and\na maximum score of 100, indicating high disability. All items of a scale must be\nanswered to be able to calculate a scale score. The only exception is the scale\nsexual intercourse, where each item may be relevant independently of the other\nitems of the same scale. Thus, the scale score for the scale sexual intercourse\nis calculated by omitting items which are not relevant.\nThe Norwegian language has two distinct written varieties, “bokmål” and “nynorsk.” 20  “Bokmål” is the most commonly used variety. The EHP-30 was therefore\ntranslated to “bokmål.” The translation and cultural adaptation of the NO-EHP-30\nwas conducted by Oxford outcomes according to recommended guidelines, 21  (Supplementary material 1).\nThe Short form-36 is a generic PROM of HRQoL composed of 36 items, one item\nassessing health change and 35 items assessing eight health concepts\nrepresenting eight scales: physical functioning (10 items), role limitations due\nto physical problems (4 items), bodily pain (2 items), general health\nperceptions (5 items), vitality (4 items), social functioning (2 items), role\nlimitations due to emotional problems (3 items), and mental health (5\nitems). 19 , 22  All scales can achieve a minimum score of 0, indicating\nworst possible health, and a maximum score of 100, indicating best possible\nhealth. QualityMetric Health Outcomes TM  Scoring Software 4.5 from\nOptumInsight Life Sciences, Inc, was used to score SF-36v2.\nCorrelation coefficients play a central role in this study. We used Fisher’s z\ntransformation to estimate 95% confidence interval for a correlation coefficient\n r . 23  The confidence interval for a correlation coefficient  r \nis widest when  r  = 0.50. We consider it sufficient with a\nprecision of ±0.10, that is, when the length of the confidence interval for\n r  is at most 0.20. 10  For a correlation coefficient of 0.50 with a sample of 150 patients, this\nconfidence interval will be 0.40–0.60. We therefore decided to include at least\n150 women with endometriosis in our study.\nConstruct validity, reliability, and interpretability of the NO-EHP-30 were\nassessed. We used the taxonomy, terminology, and definitions of measurement\nproperties suggested by the COSMIN study. 24  Hypotheses-testing was specified as assessment of convergent validity\nwhere it could be misinterpreted as hypotheses-testing associated with factor\nanalysis. Reliability was specified as test–retest reliability where it was\nthought to increase clarity. All analyses were performed with IBM SPSS\nStatistics, version 22.\nExploratory factor analysis was used to assess structural validity. 25  Principal components analysis with varimax rotation was used to\nidentify the different potential components with eigenvalues greater than 1. 26  Items with factor loadings ⩾0.40 in a factor were included in the\nfactor.\nSF-36v2 was used for hypotheses-testing to assess convergent\nvalidity. 17 , 27 , 28  We hypothesized the strongest correlations between\nEHP-30 pain and SF-36v2 bodily pain, and EHP-30 emotional well-being and\nSF-36v2 mental health. We further expected a strong correlation between\nEHP-30 social support and SF-36v2 social functioning, and EHP-30 work life\nand SF-36v2 role-physical. After obtaining the results of the factor\nanalyses, we hypothesized a strong correlation between EHP-30 control &\npowerlessness and SF-36v2 bodily pain, and EHP-30 relationship with children\nand SF-36v2 role-physical. Associations between scales of the EHP-30 and the\nSF-36v2 were calculated by Spearman’s rho correlation coefficient. There are\nno widely accepted criteria for defining a strong versus moderate versus\nweak correlation. 29  Values 0.20–0.39 were considered to indicate weak correlations,\nvalues 0.40–0.59 moderate, values 0.60–0.79 strong, and values 0.80–1.00\nvery strong correlations.\nCronbach’s alpha and corrected item-total correlations were used to measure\ninternal consistency. Cronbach’s alpha above 0.70 were considered to\nindicate acceptable internal consistency reliability for group comparisons,\nand values above 0.90 for individual comparisons. 28  Item-total correlations were corrected for overlap by omitting the\nitem from the parent scale total. Item-total correlations above 0.40 were\nconsidered to indicate acceptable internal consistency. 30\nIntraclass correlation coefficients for agreement and paired t-tests were\nused to measure test–retest reliability. Intraclass correlation coefficients\nabove 0.70 were considered to indicate acceptable reliability for group\ncomparisons, and values above 0.90 for individual measurements over\ntime. 28 , 31  Significant differences in mean scores\n(p < 0.05) were considered to indicate poor reliability. No significant\ndifferences in mean scores were considered to indicate acceptable\nreliability.\nData completeness, mean scores and standard deviations, floor and ceiling\neffects, and skewness of score distribution were used to describe the\ndistribution of item responses. 17  Floor or ceiling effects were considered present if more than 15% of\nrespondents scored the minimum value of 0 or the maximum value of 100, respectively. 31\nThis study was approved by the Regional Committee for Medical and Health Research\nEthics, division south-eastern Norway (trial registration number:\n2011/2213/Regional Committee for Medical and Health Research Ethics, division\nsouth-eastern Norway B).\n\nInitially, 150 sets of questionnaires were sent to a random sample of members of the\nNorwegian Endometriosis Association. Of these, 60 questionnaires were successfully\ncompleted and returned. Based on this preliminary response rate, an additional 225\nsets of questionnaires were sent to a second random sample of members of the\nNorwegian Endometriosis Association not contacted in the first round. In total, 162\nof 375 questionnaires were successfully completed and returned. Five of these were\nfrom women with endometriosis who reported that their diagnosis had not been\nconfirmed surgically. These were excluded. Among the 157 included respondents, 94\ncompleted and returned a second questionnaire at a later date. Of these, 10 reported\nchange in treatment or starting new treatment since completing the first\nquestionnaire. Excluding these, test–retest reliability of the NO-EHP-30 could be\nassessed in 84 of the respondents. The median number of days between answering the\nfirst and second questionnaire was 34 (range 7–168). Of the 84 respondents, 61\nreported either having menstruation when answering both questionnaires or not having\nmenstruation when answering both questionnaires. Of the 84 respondents, 15 reported\nhaving menstruation when answering one questionnaire, and not having menstruation\nwhen answering the other. The characteristics of the participants are presented in\n Table 1 .\nBasic characteristics of the participants (n = 157).\nBMI: body mass index; SD: standard deviation.\nFactor analysis of the 30 items of the core questionnaire suggested three\nfactors, explaining 70.2% of the total variance. The three-factor model\nresulted in 20 items loading on the hypothesized scales and 10 items loading\non alternative scales ( Table 2 ). Factor analysis of the 23 items of the modular\nquestionnaire suggested five factors, explaining 100% of the total variance.\nThe five-factor model resulted in 15 items loading on the hypothesized\nscales and 8 items loading on alternative scales ( Table 3 ).\nFactor analysis of the 30 items of the EHP-30 core questionnaire\nsuggesting a three-factor model.\nEHP-30: Endometriosis Health Profile-30.\nPrincipal components analysis with varimax rotation. Only factor\nloadings ⩾0.40 are shown.\nIn the original EHP-30, items 1–11 belong to the scale “pain,”\nitems 12–17 to the scale “control & powerlessness,” items\n18–23 to the scale “emotional well-being,” items 24–27 to the\nscale “social support,” and items 28–30 to the scale\n“self-image.”\nFactor analysis of the 23 items of the EHP-30 modular questionnaire\nsuggesting a five-factor model.\nEHP-30: Endometriosis Health Profile-30.\nPrincipal components analysis with varimax rotation. Only factor\nloadings ⩾0.40 are shown.\nIn the original EHP-30, items A1-5 belong to the scale “work\nlife,” items B1-2 to the scale “relationship with children,”\nitems C1-5 to the scale “sexual intercourse,” items D1-4 to the\nscale “medical profession,” items E1-3 to the scale “treatment,”\nand items F1-4 to the scale “infertility.”\nCorrelations between scales of the EHP-30 and the SF-36v2 ranged from −0.63\nto −0.81 ( Table\n4 ). The correlations are negative because the EHP-30 and the\nSF-36v2 are scored in opposite directions. All hypotheses were\nconfirmed.\nConvergent validity. Correlations between some EHP-30 scales and\nrelevant SF-36v2 scales.\nEHP-30: Endometriosis Health Profile-30; SF-36v2: Short Form-36\nversion 2.\nCronbach’s alpha ranged from 0.87 to 0.96 for the original scales of the core\nquestionnaire and from 0.78 to 0.94 for the original scales of the modular\nquestionnaire (supplementary material 2). The corrected item-total\ncorrelation coefficients ranged from 0.45 (item 23) to 0.91 for the original\nscales of the core questionnaire and from 0.55 to 0.89 for the original\nscales of the modular questionnaire.\nIntraclass correlation coefficient for test–retest agreement ranged from 0.80\nto 0.85 for the scales of the core questionnaire, and from 0.67 to 0.91 for\nthe scales of the modular questionnaire ( Table 5 ). The mean scale scores did\nnot differ significantly between the first and second measurements.\nTest–retest reliability analysis including only the 61 respondents reporting\neither having or not having menstruation when answering both questionnaires,\ndid not alter the general findings (data not shown).\nTest–retest reliability and intraclass correlation coefficients (ICC)\nwith 95% confidence intervals (CI) for test–retest agreement.\nComparison of mean scale scores at time 1 and time 2 with\np-values.\nICC: intraclass correlation coefficient; EHP-30: Endometriosis\nHealth Profile-30; CI: confidence interval.\nEach ICC was significantly different from zero\n(p < 0.001).\nPaired samples t-test, significance two-tailed.\nThe results are presented in  Table 6 . Data completeness of at least 97.5% was achieved for all\nEHP-30 scales. The proportion of participants to whom each scale of the modular\nquestionnaire was relevant, varied from 39.4% (the scale infertility) to 87.2%\n(the scale sexual intercourse). Floor effect was only found for the scale\nself-image (20.1%) in the core questionnaire, and for the scales work life\n(33.9%), relationship with children (34.2%), and medical profession (20.5%) in\nthe modular questionnaire. No ceiling effects were observed. Skewness was low\nfor all the scales.\nInterpretability. Data completeness, mean scores and standard deviations\n(SD), floor and ceiling effects, and skewness of score distribution.\nN/R: not relevant; N/A: not applicable; EHP-30: Endometriosis Health\nProfile-30.\nNumber of participants for whom the scale was not relevant (only\napplicable for the modular questionnaire).\n\nFactor analysis suggested a three-factor model for the EHP-30 core questionnaire, in\ncontrast to the original five-factor model. Items of the scales pain and control\n& powerlessness loaded on the same factor. A similar finding was demonstrated in\nthe original, Portuguese, and French version EHP-30. 9 , 14 , 15  As argued by the developers,\nit is likely that pain has considerable impact on sense of control and\npowerlessness. In this study, assessment of convergent validity demonstrated strong\ncorrelations between each of the EHP-30 scales pain and control & powerlessness\nand the SF-36v2 scale bodily pain, supporting this interpretation. Strong\ncorrelations were also demonstrated between the EHP-30 scales emotional well-being\nand social support and the corresponding SF-36v2 scales mental health and social\nfunctioning. Thus, the findings in this study support construct validity of four of\nfive scales (pain, control & powerlessness, emotional well-being, and social\nsupport) of the core questionnaire.\nThe fifth scale of the core questionnaire, self-image, consists of three items. The\nfirst two items concern the effect of endometriosis on choice of clothing and\nappearance, and the last item concerns the effect of endometriosis on\nself-confidence. In factor analysis, the first two items loaded on the scale social\nsupport, and the last item loaded on the scale emotional well-being. Thus, the\nconstruct self-image does not seem to be measured appropriately by the NO-EHP-30.\nThe lack of association between appearance and self-confidence is likely not\nexclusive to the Norwegian culture. Subtle differences in exploratory factor\nanalysis technique, that is, performed with or without predefinition of five factors\nfor the core questionnaire, may have masked a similar finding in other translated\nversions. 14 , 25\nFactor analysis suggested a five-factor model for the EHP-30 modular questionnaire,\nin contrast to the original six-factor model. Factor analysis of the modular\nquestionnaire has been performed for the original and French version\nEHP-30. 9 , 15  In this study, items of the scales work life and relationship\nwith children loaded on the same factor. A similar finding was demonstrated in the\noriginal version, but not in the French version. 9 , 15  These discrepancies may be due\nto difference in daily patterns of work life and child care in these three\ncountries. In this study, factor analysis could not support construct validity of\nthe scale treatment. The three items of the scale treatment loaded on three separate\nfactors. A tendency of the first item of the scale treatment to load on a different\nfactor than the two latter items has been demonstrated by factor analysis with\nlarger samples in both the original and French version EHP-30. 9 , 15\nThe NO-EHP-30 demonstrated acceptable test–retest reliability except for the scale\nrelationship with children of the modular questionnaire, which demonstrated an\nintraclass correlation coefficient of 0.67. Although the time interval between\nanswering the first and second questionnaire likely was long enough to minimize\nmemory effects, it may have allowed changes in the status of the subject. 32  Exclusion of questionnaires from respondents reporting change in treatment or\nstarting new treatment between assessments, probably reduced this effect. Phase of\nmenstruation did not seem to affect the outcome. The scale relationship with\nchildren consists of two items. The second item concerns the ability to play with\nchild/children and implies children of younger age. In the case of children of\nyounger age, the score of this scale may depend not only on the health status of the\nrespondent but also on the health status of the child/children. Thus, this\nparticular scale may be less reliable.\nThis study is the first to evaluate both test–retest reliability and validity of the\ncore questionnaire of the EHP-30 including adequate sample sizes. 18 , 33  Regarding the\nmodular questionnaire, the varying relevance of scales to participants has likely\nrendered some sample sizes inadequate. To ensure adequate sample size for the least\nrelevant modular questionnaire scale, the general sample size should have been three\ntimes larger. On the other hand, these variations in relevance of the scales of the\nmodular questionnaire, would limit the use of the modular questionnaire in most\nresearch settings. Another weakness of this study is the lack of representativeness\nof the endometriosis patient group. Participants were recruited from a patient\nassociation. Thus, participants with severe forms of endometriosis are likely overrepresented. 34  Recruiting a representative sample of women with endometriosis is a challenge\nin almost all research settings. Most, if not all, of the EHP-30 validation studies\nhave recruited participants from patient associations and/or from secondary or\ntertiary referral centers. 10 – 15  Thus, participants with severe\nforms of endometriosis are likely overrepresented in all studies, although in\nvarying degree. Moreover, patients attending secondary and tertiary referral centers\nare more likely to be in active disease and treatment settings, making test–retest\nreliability analysis difficult. Endometriosis registries would have been a\npreferable recruitment source to endometriosis associations. However, no\nendometriosis registry is established in Norway. Furthermore, the responsiveness of\nthe NO-EHP-30 was not evaluated.\nThe construct self-image does not seem to be measured appropriately by the NO-EHP-30,\nsuggesting a lack of cross-cultural validity of the EHP-30. With multinational and\nmulticultural studies increasing, this study underlines the importance of adequate\ntranslation, cross-cultural adaptation, and cross-cultural validation of PROMs.","source_license":"CC0","license_restricted":false}