Reviewer’s report
Title:  The Endometriosis Impact Questionnaire (EIQ): a tool to measure the long-term impact of  
endometriosis on different aspects of women's lives
Version: 0 Date: 02 Oct 2018
Reviewer: Lee A. Learman
Reviewer's report:
The authors describe the psychometric development of the Endometriosis Impact Questionnaire (EIQ),  
which  was  created  to  provide  a  more  comprehensive  multi-domain  assessment  of  impact  than  
previously published questionnaires.   The  manuscript  address  the  most  important  aspects  of  tool  
development and provides reliability and validity evidence in support of the EIQ.  The paper is well  
organized and clearly written, with a useful figure depicting the steps and phases of questionnaire  
development and refinement.  I have several suggestions for the authors.
(1) Declarations of validity: the contemporary understanding of questionnaire validity has evolved  
away from inferences based on single studies to a body of evidence established over time with different  
subjects in different settings and different sets of comparative data.   We now speak in a single study of  
"establishing validity evidence" instead of declaring a new questionnaire to be "valid" or to have been  
"validated".   Reliability is treated differently because it can be estimated with specific data sets and  
then reproduced in other samples, but does not require an evolving body of evidence.  For more  
information see Cook DA et al, A contemporary approach to validity arguments: a practical guide to  
Kane's framework.: Med Educ. 2015 Jun;49(6):560-75.
Throughout the abstract and manuscript the wording should be modified accordingly.  For example, in  
the Abstract:  Line 45 should state "good evidence of concurrent validity".  The conclusions on lines  
47-50 should omit "valid" from the first sentence and change the second sentence to "We recommend  
additional studies to establish validity evidence for the EIQ, including studies in other countries and  
languages."    Line  70  (page  3)  should  be  modified  from  "the  only  validated  disease-specific  
questionnaire to measure the HRQoL" to "the disease-specific questionnaire to measure the HRQoL  
with the strongest validity evidence."  Similar changes should be made throughout the manuscript when  
validity is mentioned. 
(2) Interpretation of factor analysis results, comparison with predefined impact domains: The final EIQ  
includes 6 dimensions based upon exploratory factor analysis.  It isn't clear how the factor analysis  
results relate to the construct being measured.  Are the 6 dimensions identified in the factor analysis  
consistent with a conceptual framework that was developed from the literature review?  Were the  
authors surprised that the first dimension (Physical-psychosocial) was much larger than the others and  
did not end up pas 3 separate dimensions for physical (13 items), psychological (16 items) and social (4  
items) impact?  It would be helpful to include a statement regarding how the impact domains were  
defined from the literature review and focus groups, and to discuss how the predefined domains  
compared to the factor analysis results.   
(3) In the Discussion's Limitations section (line 363-) it should be noted that, other than self-reported  
surgically diagnosed endometriosis, endometriosis-related symptoms and treatments, pregnancy history  
and delayed fertility, the current study did not collect other important clinical information regarding the  
severity of endometriosis lesions and the existence of comorbidities that could also contribute to  
symptoms, such as mood disorders, obesity, musculoskeletal and neuropathic sources of pain.  These  
conditions are not uncommon in patients who have endometriosis.  Not knowing these key clinical  
characteristics of the sample limits the generalizability of the authors' findings.  
(4) In the Conclusions section (line 371-), further validity evidence should also be recommended in  
clinically  relevant  subgroups  of  endometriosis  patients,  such  as  women  presenting  for  fertility  
evaluations versus women presenting with chronic pelvic pain, as well as endometriosis patients with  
the comorbid conditions listed in my comment #3.  This is just as important as studies in other  
countries and languages.
Are the methods appropriate and well described?
If not, please specify what is required in your comments to the authors.
Yes
Does the work include the necessary controls?
If not, please specify which controls are required in your comments to the authors.
Yes
Are the conclusions drawn adequately supported by the data shown?
If not, please explain in your comments to the authors.
Yes
Are you able to assess any statistics in the manuscript or would you recommend an additional  
statistical review?
If  an  additional  statistical  review  is  recommended,  please  specify  what  aspects  require  further  
assessment in your comments to the editors.
I am able to assess the statistics
Quality of written English
Please indicate the quality of language in the manuscript:
Acceptable
Declaration of competing interests
Please complete a declaration of competing interests, considering the following questions:
1. Have you in the past five years received reimbursements, fees, funding, or salary from an  
organisation  that  may  in  any  way  gain  or  lose  financially  from  the  publication  of  this  
manuscript, either now or in the future?
2. Do you hold any stocks or shares in an organisation that may in any way gain or lose financially  
from the publication of this manuscript, either now or in the future?
3. Do  you  hold  or are  you  currently applying  for  any patents  relating  to  the  content  of  the  
manuscript?
4. Have you received reimbursements, fees, funding, or salary from an organization that holds or  
has applied for patents relating to the content of the manuscript?
5. Do you have any other financial competing interests?
6. Do you have any non-financial competing interests in relation to this paper?
If you can answer no to all of the above, write 'I declare that I have no competing interests' below. If  
your reply is yes to any, please give details below.
I declare that I have no competing interests.
I agree to the open peer review policy of the journal. I understand that my name will be included on my  
report to the authors and, if the manuscript is accepted for publication, my named report including any 
attachments I upload will be posted on the website along with the authors' responses. I agree for my 
report to be made available under an Open Access Creative Commons CC-BY license 
(http://creativecommons.org/licenses/by/4.0/ ). I understand that any comments which I do not wish to 
be included in my named report can be included as confidential comments to the editors, which will not  
be published.
I agree to the open peer review policy of the journal