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With no validated measure for communication in CDD, this study evaluated the psychometric properties of the Communication and Symbolic Behavior Scales-Developmental Profile Infant Toddler Checklist (CSBS\u2013DP ITC). Caregivers (n\u2009=\u2009150; affected individuals aged 1\u201329\u00a0years) completed the CSBS-DP ITC. Distribution of scores indicated a floor effect. There was poor divergent validity for the three-factor model but goodness of fit and convergent validity data were satisfactory for the one-factor model. Individuals with poorer overall functional abilities scored lower on the CSBS-DP ITC. Test\u2013retest reliability was excellent. The floor effect could explain the very high reliability, suggesting problems as a sensitive outcome measure in clinical trials for CDD.<\/jats:p>","DOI":"10.1007\/s10803-023-06002-w","type":"journal-article","created":{"date-parts":[[2023,5,15]],"date-time":"2023-05-15T14:21:23Z","timestamp":1684160483000},"page":"2526-2535","update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":10,"title":["Validating the Communication and Symbolic Behavior Scales\u2013Developmental Profile Infant\u2013Toddler Checklist (CSBS\u2013DP ITC) Beyond Infancy in the CDKL5 Deficiency Disorder"],"prefix":"10.1007","volume":"54","author":[{"given":"Jacinta","family":"Saldaris","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Helen","family":"Leonard","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kingsley","family":"Wong","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Peter","family":"Jacoby","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mary","family":"Spence","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Eric D.","family":"Marsh","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tim A.","family":"Benke","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Scott","family":"Demarest","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7358-9037","authenticated-orcid":false,"given":"Jenny","family":"Downs","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2023,5,15]]},"reference":[{"key":"6002_CR1","doi-asserted-by":"publisher","unstructured":"Berg, A. 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Ethics approval for this study was provided by Human Research Ethics Committees at The University of Western Australia (RA\/4\/20\/6198; 2020\/ET000271) and primary caregivers provided informed consent to participate in the study.","order":2,"name":"Ethics","group":{"name":"EthicsHeading","label":"Ethics approval and consent to participate"}},{"value":"Helen Leonard: Consultancy for Marinus, Acadia, Newron, Orion, Anavex, GW Pharmaceuticals, Neurogene and AveXis; Clinical Trials with Newron and Anavex; All remuneration has been made to her department. Tim A. Benke: Consultancy for AveXis, Ovid, GW Pharmaceuticals, International Rett Syndrome Foundation, Takeda, and Marinus; Clinical Trials with Acadia, Ovid, GW Pharmaceuticals, Marinus and RSRT; All remuneration has been made to his department. Scott Demarest: Consultancy for Upsher-Smith, Biomarin and Neurogene, Marinus and Ovid Therapeutics; All remuneration has been made to his department. Eric D. Marsh: Consultancy for Stoke therapeutics, Cipla pharmaceuticals. Clinical trials with Acadia, GW pharma, Marinus, RSRT, Biopharm, Stoke therapeutics, Zogenix Pharmaceuticals. Jenny Downs: Consultancy for Marinus, Acadia, Orion, Taysha, Neurogene and AveXis; Clinical Trials with Newron and Anavex; All remuneration has been made to her department. Each of these disclosures relate to subject matter not contained in this manuscript. Peter Jacoby, Jacinta Saldaris, Kingsley Wong, and Mary Spence report no disclosures or conflicts of interest.","order":3,"name":"Ethics","group":{"name":"EthicsHeading","label":"Competing interests"}}]}}