Evaluation of the Intermittent Exotropia Questionnaire Using Rasch Analysis

Importance  The Intermittent Exotropia Questionnaire (IXTQ) is a patient, proxy, and parental report of quality of life specific to children with intermittent exotropia. We refine the IXTQ using Rasch analysis to improve reliability and validity.

Observation  Rasch analysis was performed on responses of 575 patients with intermittent exotropia enrolled from May 15, 2008, through July 24, 2013, and their parents from each of the 4 IXTQ health-related quality-of-life questionnaires (child 5 through 7 years of age and child 8 through 17 years of age, proxy, and parent questionnaires). Questionnaire performance and structure were confirmed in a separate cohort of 379 patients with intermittent exotropia. One item was removed from the 12-item child and proxy questionnaires, and response options in the 8- to 17-year-old child IXTQ and proxy IXTQ were combined into 3 response options for both questionnaires. Targeting was relatively poor for the child and proxy questionnaires. For the parent questionnaire, 3 subscales (psychosocial, function, and surgery) were evident. One item was removed from the psychosocial subscale. Resulting subscales had appropriate targeting.

Conclusions and Relevance  The Rasch-revised IXTQ may be a useful instrument for determining how intermittent exotropia affects health-related quality of life of children with intermittent exotropia and their parents, particularly for cohort studies.

The Intermittent Exotropia Questionnaire (IXTQ) is a patient-derived, intermittent exotropia–specific instrument designed to evaluate health-related quality of life (HRQOL) in children with intermittent exotropia and their parents.^1,2 The IXTQ consists of 3 parts: the 12-item child IXTQ (completed by the child to assess the child’s HRQOL), the 12-item proxy IXTQ (completed by the parent to assess the child’s HRQOL), and the 17-item parent IXTQ (completed by the parent regarding his or her own HRQOL).¹ The child and proxy questionnaires each have a single subscale. The parent questionnaire contains 3 subscales: psychosocial, function, and surgery. The IXTQ is reliable and valid for assessing HRQOL in children with intermittent exotropia.^1-3 It is available for download free of charge at http://pedig.jaeb.org/.

The IXTQ was originally developed using classical test theory. Rasch analysis may be used to modify and improve existing HRQOL instruments.^4-9 In the present study, Rasch analysis was used to refine the existing IXTQ, removing items that do not contribute meaningful information to the instrument and ensuring that response options are properly interpreted.

Parents gave written informed consent, and children gave written assent when required. The protocol was approved by the institutional review boards of the Mayo Clinic, Jaeb Center for Health Research, and other local sites involved in the study. Data were collected and analyzed in accordance with the Health Insurance Portability and Accountability Act guidelines.

The IXTQ was completed by 575 parents of 575 children aged 1 through 16 years with intermittent exotropia at the time of their child’s clinic examination, enrolled from May 15, 2008, through July 24, 2013. The 295 children aged 5 years or older completed the age-appropriate child IXTQ. Parents and children completed the IXTQ as part of routine care in the strabismus practice of one of the authors (J.M.H., n = 110) or at the enrollment examination for 1 of 2 ongoing randomized clinical trials being conducted by the Pediatric Eye Disease Investigator Group (NCT 01032603 [n = 69] and NCT 01032330 [n = 396]). Child questionnaires were administered to children aged 5 through 7 years by study personnel. All 8- to 17-year-old child, proxy, and parent questionnaires were self-administered. Patient demographics are reported in eTable 1 in the Supplement.

Before Rasch analysis, items with floor and ceiling effects on the child, proxy, and parent IXTQs were eliminated as described in the eMethods in the Supplement. Rasch analysis was performed on each of the 4 IXTQs using the analytic methods that we have applied previously (eMethods in the Supplement).⁹ The performance and structure of the Rasch-modified IXTQ were confirmed with a separate Rasch analysis using IXTQ data from an additional 379 parents and their children (eTable 1 in the Supplement).

Detailed results are available in the eResults and eTables 2 through 9 in the Supplement. Item 12 was removed from the child and proxy IXTQs because of strong ceiling effects (Table 1). Rasch analysis on the remaining items indicated that performance of the 8- to 17-year-old child IXTQ and proxy IXTQ would be enhanced by reducing the number of response options to 3 categories. Properties of dimensionality, response ordering, local dependence, misfit, and differential item functioning were acceptable (eResults, eFigure 1, and eTables 2, 4, 5, and 6 in the Supplement), although targeting was not ideal (Figure).

For the parent IXTQ, no strong floor or ceiling effects were noted (Table 2). The 3 previously identified subscales for the parent IXTQ (psychosocial, function, and surgery) were confirmed with principal component analyses (eResults and eTables 3 and 4 in the Supplement). For each subscale, properties of dimensionality, response ordering, local dependence, misfit, and differential item functioning were acceptable with the exception of notable misfit for item 17 in the parent psychosocial subscale, which was then removed (eResults, eFigure 2, and eTables 3, 4, 5, and 7 in the Supplement). Targeting of all 3 parent IXTQ subscales was acceptable (Figure).

Applying the Rasch modifications derived in the present study to a separate cohort of 379 patients, the factor structure and evaluative properties of the IXTQ were confirmed (eResults and eTables 8 and 9 in the Supplement).

The results of Rasch analysis indicated that the IXTQ would benefit from slight response option restructuring and item removal (removal of item 12 from the child and proxy IXTQs, reducing the number of response options on the 8- to 17-year-old child IXTQ and the proxy IXTQ from 5 to 3 options, removing item 17 from the parent psychosocial subscale, and scoring the 3 parent subscales separately). These modifications were confirmed to yield unidimensional domains in a separate cohort, with relatively poor targeting for the child and proxy questionnaires but good targeting and person separation for the parent function, psychosocial, and surgery subscales.

Because the 8- to 17-year-old child IXTQ response options can be collapsed to 3 from 5, it may be possible to combine the 5- to 7-year-old child IXTQ with the 8- to 17-year-old child IXTQ in future versions of the child IXTQ with 3 response options. Nevertheless, combining the 2 forms of the child IXTQ would require changing the wording of one of the questionnaires from second to first person or vice versa, requiring all children aged 5 through 17 years to complete the questionnaire on their own or to have the questionnaire read to all children regardless of age. Such changes would require additional validation.

The person separation index and reliability of the child and proxy IXTQs are less than ideal. In contrast, the person separation index and reliability for each of the parent IXTQ subscales are appropriate. Despite this limitation, there may be value in using the child and proxy questionnaires in cohort studies because group summary scores are less sensitive to noise.

There was poor targeting for the child and proxy questionnaires. One potential reason for this poor targeting is the low level of expressed concern on the part of the children and, similarly, the low level of concern expressed by the parents as proxy for their children.

We now recommend that the parent IXTQ be Rasch scored and reported only as 3 separate subscale scores rather than a composite as scored previously.^1,3,10 We have created conversion tools using Excel spreadsheets (Microsoft Inc) to easily convert raw IXTQ responses to Rasch-scaled responses and have made them available online (http://pedig.jaeb.org/). In addition to logit values, the lookup tool converts each Rasch person measure from a logit value to a 0 to 100 value (0 indicating worst HRQOL and 100 indicating best HRQOL) through a linear transformation of the person scores. The Rasch-revised IXTQ, in particular the parent IXTQ, provides a valuable tool to measure the effect of intermittent exotropia on children and their parents.

Submitted for Publication: July 8, 2014; final revision received November 13, 2014; accepted November 13, 2014.

Corresponding Author: Jonathan M. Holmes, BM, BCh, Department of Ophthalmology, Mayo Clinic, 200 First St SW, Rochester, MN 55905 (holmes.jonathan@mayo.edu).

Published Online: January 29, 2015. doi:10.1001/jamaophthalmol.2014.5622.

Author Contributions: Dr Holmes and Mr Leske had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Study concept and design: Leske, Holmes.

Acquisition, analysis, or interpretation of data: All authors.

Drafting of the manuscript: Leske, Holmes.

Critical revision of the manuscript for important intellectual content: All authors.

Statistical analysis: All authors.

Obtained funding: Holmes.

Administrative, technical, or material support: Leske, Holmes.

Study supervision: Holmes.

Conflict of Interest Disclosures: All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest and none were reported.

Funding/Support: The study was supported by grants EY018810 (Dr Holmes), EY024333 (Dr Holmes), and EY011751 (Jaeb Center for Health Research) from the National Institutes of Health, Research to Prevent Blindness (Dr Holmes as the Olga Keith Weiss Scholar and an unrestricted grant to the Department of Ophthalmology, Mayo Clinic), and the Mayo Foundation.

Role of the Funder/Sponsor: The funding sources had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and the decision to submit the manuscript for publication.

Previous Presentation: This study was presented in part at the Association for Vision in Research and Ophthalmology Annual Meeting; May 9, 2012; Fort Lauderdale, Florida.

Pediatric Eye Disease Investigator Group: Clinical sites are listed in order by number of subjects enrolled in the studies. Personnel are listed as primary investigator (PI), investigator (I), and coordinator (C). Tomball, TX—Houston Eye Associates: Aaron Miller (PI), Jorie Jackson (C); West Des Moines, IA—Wolfe Clinic: Donny Suh (PI), Susan Hayes (C); Rockville, MD—Stephen R. Glaser, MD, PC: Stephen Glaser (PI), Monica Pacheco (I), Laura Graham (C); Houston, TX—Baylor College of Medicine, Texas Children’s Hospital—Department of Ophthalmology: Evelyn Paysse (PI), Kimberly Yen (I), Mohamed Hussein (I), Paul Steinkuller (I), David Coats (I), Lingkun Kong (C); Nashville TN—Vanderbilt Eye Center: Sean Donahue (PI), David Morrison (I), Lori Ann Kehler (I), Robert Estes (I), Lisa Fraine (C); Salt Lake City, UT—Rocky Mountain Eye Care Associates: David Petersen (PI), J. McMurtrey (C); Erie, PA—Pediatric Ophthalmology of Erie: Nicholas Sala (PI), Jeanine Romeo (C): Norfolk, VA—Eastern Virginia Medical School: Earl Crouch (PI), Earl Crouch III (I), Gaylord Ventura (C); Rochester MN—Mayo Clinic: Jonathan Holmes (PI), Brian Mohney (I), Tomohiko Yamada (I), David A. Leske (C), Sarah Hatt (C), Rebecca Nielsen (C), Laura Liebermann; Montreal, Quebec, Canada—Centre Hospitalier Universitaire Sainte-Justine: Rosanne Superstein (PI), Caroline Belanger (I), Nicole Fallaha (I), Maryse Thibeault (C); Chicago Ridge, IL—The Eye Specialists Center, LLC: Benjamin Ticho (PI), Alexander Khammar (I), Megan Allen (I), Deborah Clausius (C); Cranberry Township, PA—Everett and Hurite Ophthalmic Association: Darren Hoover (PI), Pamela Huston (C); Durham, NC—Duke University Eye Center: Laura Enyedi (PI), David Wallace (I), Tammy Yanovitch (I), Sarah Jones (C); Lancaster, PA—Family Eye Group: David Silbert (PI), Noelle Matta (C); Winston-Salem, NC—Wake Forest University: Richard Weaver (PI), Eric Hein (I), Lori Cooke (C); Atlanta, GA—The Emory Eye Center: Scott Lambert (PI), Phoebe Lenhart (I), Amy Hutchinson (I), Judy Brower (C); Birmingham, AL—University of Alabama at Birmingham School of Optometry: Robert Rutstein (PI), Wendy Marsh-Tootle (I), Katherine Weise (I), Marcela Frazier (I), Ross Roegner (C); Fullerton, CA—Southern California College of Optometry: Susan Cotter (PI), Angela Chen (I), Carmen Barnhardt (I), Kristine Huang (I), Paula Handford (I), Reena Patel (I), Catherine Heyman (I), Raymond Chu (I), Lernik Mesropian (I), Susan Parker (C); Miami, FL—Bascom Palmer Eye Institute: Susanna Tamkins (PI); Albuquerque, NM—Children’s Eye Center of New Mexico: Todd Goldblum (PI), Kenneth Adams (I), Angela Alfaro (C); Concord, NH—Concord Eye Care PC: Christie Morse (PI), Maynard Wheeler (I), Melanie Christian (C); Minneapolis, MN—University of Minnesota: C. Gail Summers (PI), Jill Anderson (I), Erick Bothun (I), Inge De Becker (I), Sarah Downes (I), Ann Holleschau (C); Gainesville, FL—University of Florida Shands Hospital: Nausheen Khuddus (PI), Tammy Price (C); Chicago, IL—Ann & Robert H. Lurie Children’s Hospital of Chicago: Bahram Rahmani (PI), Hawke Yoon (I), Yana Kiesau (I), Aaliyah Hamidullah (C); Durham, NC—North Carolina Eye, Ear, & Throat: Joan Roberts (PI), Heather Klem (C); Kingston, Ontario, Canada—Queen’s University Department of Ophthalmology: Brian Arthur (PI), Lesley MacSween (C); Calgary, Alberta, Canada—Alberta Children’s Hospital: William Astle (PI), Kenneth Romanchuk (I), Emi Sanders (C); New York, NY—State University of New York, College of Optometry; Robert Duckman (PI), Marilyn Vricella (I), Sara Meeder (C); Lisle, IL—Progressive Eye Care: Patricia Davis (PI), Indre Rudaitis (C); Charleston, SC—Medical University of South Carolina, Storm Eye Institute: Mae Peterseim (I), Ronald Teed (I), Carol Bradham (C); Baltimore, MD—Greater Baltimore Medical Center; Mary Louise Collins (PI), Allison Jensen (I), Maureen Flanagan (C); Portland, OR—Casey Eye Institute: Daniel Karr (PI), Allison Summers (I), Ann Stout (I), Paula Rauch (C); Chicago, IL—Illinois College of Optometry: Yi Pang (PI), Megan Allen (I), Anesu Mvududu (C); Aberdeen, NC—Family Eye Care of the Carolinas: Michael Bartiss (PI), Tennille McGaw (C); Cleveland, OH—Rainbow Babies & Children’s Hospital Department of Ophthalmology: Faruk Ogre (PI), Beth Colon (C); Philadelphia, PA—Salus University/Pennsylvania College of Optometry: Mitchell Scheiman (PI), Karen Pollack (C); Boston, MA—Boston Medical Center: Jean Ramsey (PI), Stephen Christiansen (I), Elise Harb (I), Vanessa Vazquez (C); Houston, TX—University of Houston College Optometry: Ruth E. Manny (PI), Karen D. Fern (I), Catherine McDaniel (I), Heather Anderson (I), Joan Do (C); Kansas City, MO—Children’s Mercy Hospitals and Clinics: Adriana Grigorian (I), Rebecca Dent (C); Bronx, NY—Montefiore Medical Center: Ilana Friedman (PI), Evelyn Koestenblatt (C); Halifax, Nova Scotia, Canada—Izaak Walton Killam Health Centre: G. Robert LaRoche (PI), Stephen Van Iderstine (C); Baltimore, MD—Wilmer Ophthalmological Institute, John Hopkins University: Michael X. Repka (PI), Hee-Jung Park (I), Xiaonong Liu (C), Alex Christoff (C); Providence, RI—Pediatric Ophthalmology and Strabismus Associates: David Tien (PI), Samantha Garner (C); Portland, OR—Pacific University College of Optometry: Richard London (PI), Jayne Silver (C); Bloomington, IN—Indiana School of Optometry: Don Lyon (PI), Tawna Roberts (I), Vivian Wong (I), Kristy Dunlap (C); Rochester, NY—University of Rochester Eye Institute: Matthew Gearinger (PI), Peter MacDowell (C); Sacramento, CA—University of California Davis, Department of Ophthalmology: Mary O’Hara (PI), Nandini Gandhi (C); Cleveland OH—Cole Eye Institute: Elias Traboulsi (PI), Paul Rychwalski (I), Susan Crowe (C); Columbia, SC—University of South Carolina School of Medicine: Edward Cheeseman (PI), Michelle Bass (C); Spokane, WA—Spokane Eye Clinic: Jeffery Colburn (PI), Eileen Dittman (C); Iowa City, IA—University of Iowa Hospitals and Clinics: Susannah Longmuir (PI), Wanda Ottar Pfeifer (C); Indianapolis, IN—Indiana University Medical Center: Daniel Neely (PI), Michele Whitaker (C); Columbus, OH—The Ohio State University: Marjean Kulp (PI), Andrew Toole (I), Tamara Oechslin (I), Freda Dallas (C), Nancy Stevens (C); Madison, WI—University of Wisconsin, University Station: Yasmin Bradfield (PI), Barbara Soderling (C); Boston, MA—Tufts Medical Center Inc: Mitchell Strominger (PI), Shelley Klein (C); Seattle, WA—Seattle Children’s Hospital: Erin Herlihy (PI), Jennifer Brady (C); San Diego, CA—Scripps Clinic: Gregory Ostrow (PI), Laura Kirkeby (C); New York, NY—Mount Sinai School of Medicine: Tamiesha Frempong (PI), Dipali Dave (C); Los Angeles, CA—Jules Stein Eye Institute at the University of California, Los Angeles: Stacy Pineles (PI), Marianne Esguerra (C); Poland, OH—Eye Care Associates Inc: Sergul Erzurum (PI), Diana McOwen (C); Philadelphia, PA—Children’s Hospital of Philadelphia: Brian Forbes (PI), Gil Binenbaum (I), Karen Karp (C); Waterbury, CT—Eye Care Group PC: Tara Cronin (I), Cheryl Capobianco (C); Grand Rapids, MI—Pediatric Ophthalmology PC: Robert Peters (I), Jan Hilbrands (C); Sharon, MA—Daniel M. Laby, MD: Daniel Laby (PI), Heidi Martin (C); Fort Lauderdale, FL—Nova Southeastern University College of Optometry, The Eye Institute: Jacqueline Rodena (I), Annette Bade (C); Buffalo, NY—Ross Eye Institute, University of Buffalo Medical School, Department of Ophthalmology: Airaj Fasiuddin (PI), Blair Spencer (C); Boston, MA—Harvard Vanguard Medical Associates: Justin Smith (PI), Mei Mellott (I), Troy Kieser (C).

PEDIG Coordinating Center: Raymond T. Kraker, Roy W. Beck, Christina M. Cagnina-Morales, Danielle L. Chandler, Laura E. Clark, Chelsea Miano, Quayleen Donahue, Brooke P. Fimbel, Nicole C. Foster, Elizabeth L. Lazar, Stephanie V. Lee, B. Michele Melia, Diana E. Rojas.

Intermittent Exotropia Study Planning Committee: Jonathan M. Holmes, (planning committee chair), Sean Donahue (protocol chair, Intermittent Exotropia Study 1), Susan A. Cotter (protocol cochair, Intermittent Exotropia Study 2), Brian G. Mohney (protocol cochair, Intermittent Exotropia Study 2), Roy W. Beck, Eileen E. Birch, Danielle L. Chandler, Stephen P. Christiansen, Sarah R. Hatt, Raymond T. Kraker, David A. Leske, Michele Melia, Mary O’Hara, Yi Pang, Michael X. Repka. Kenneth Romanchuck, Susanna M. Tamkins, David K. Wallace, David T. Wheeler.

Strabismus Steering Committee: Eileen E. Birch, Danielle L. Chandler, Stephen P. Christiansen, Susan A. Cotter, Sean Donahue, Caroline C. Fang (2011-2012), Sarah R. Hatt, Jonathan M. Holmes, Darren L. Hoover, Raymond T. Kraker, Elizabeth L. Lazar, Ryan McMurtrey (2011-2012), Michele Melia, Brian G. Mohney, Michael X. Repka, Mitchell M. Scheiman, Susanna M. Tamkins.