{"doi":"10.1002/mds.30246","title":"The Parkinson's Disease Cognitive Composite: Lessons Forgotten from Preclinical Alzheimer's Cognitive Composites","abstract":"We were intrigued by Weintraub and colleagues'1 creation of a Parkinson's disease cognitive composite (PDCC). As the authors emphasize, the goal of composites, exemplified by the Preclinical Alzheimer's Cognitive Composite (PACC), is to create a psychometrically sound index, superior in detecting and tracking disease processes for clinical trials relative to constituent scores. We agree that a composite is needed in Parkinson's disease (PD), but it requires key validation steps before the serious adoption of such applications can be considered: (1) theoretic or empiric justification behind construction; and (2) evaluation of the PDCC's reliability and meaningful clinical validation using biomarker or longitudinal outcomes. In PD, there is neither consensus around, nor widespread availability of, a biomarker as there is in Alzheimer's (AD) (eg, amyloid positivity). Further, PD has a panoply of outcomes, with cognitive decline being less prominent relative to AD. PACC construction relied on theoretical, data driven, and psychometric considerations.2, 3 For example, PACCs were developed from the cognitive domains/tests known to decline earliest in AD and were determined to have reliability, structural validity, predictive validity, and to be sensitive to change.2, 4, 5 In contrast, this PDCC's test selection was not linked to predictive measures of PD cognitive decline.6 Instead, original Parkinson's Progression Markers Initiative (PPMI) battery tests were included without theoretic justification, and subsequent PPMI additions (eg, letter fluency) that may better track or predict progression were excluded. Further, the authors' largest effect size was in a constituent task (Symbol Digit Modalities) and not the PDCC. As presented in the paper, the PDCC differs between medication naive PD patients and controls, but clinically, the PD group's z-score is within normal limits. More robust validation and clarity on other methodological ambiguities (eg, practical application of robust norms, addressing skewed residuals) are needed to support the PDCC. By not considering the concerns raised above, the utility of the composite is limited and not inherently specific to PD. To determine whether the proposed PDCC has reliability and structural validity, we reanalyzed PPMI, (n = 4075; Mage = 64.9, Meducation = 16.3, 54.8% men, 95% White) selecting a mixed cohort sample at baseline. Confirmatory factor analysis tested the internal consistency and structural validity of their PDCC. Unfortunately, it had inadequate reliability (ω = 0.64) and structural validity on all five fit indices (Table 1). We explored whether a differently weighted (vs. equally weighted) PDCC performed better and found adequate reliability (ω = 0.78) with improved fit, although still inadequate structural validity. As the authors note, assigning weights can be vexing, but the reliability and validity of weighted PACCs is typically evaluated before deciding to unweight.2, 4, 5 We demonstrate that Weintraub and colleagues'1 PDCC does not meet select psychometric criteria and we caution its further use without additional information. A sensitive and predictive PDCC is needed, however, we must incorporate lessons learned in AD research to strengthen methodology and appreciate the unique cognitive trajectories, motor influences, and clinical trial needs of PD. D.A.G.: Conceptualization, Methodology, Formal Analysis, Writing – original draft. A.J.K.: Conceptualization, Methodology, Writing – original draft. S.E.S.P.: Writing – review & editing. J.E.F.: Writing – review & editing. CGG: Conceptualization, Writing – review & editing. Data used in the preparation of this article was obtained on March 12, 2025 from the PPMI database (www.ppmi-info.org/access-data-specimens/download-data), RRID:SCR_006431. For up-to-date information on the study, visit www.ppmi-info.org. PPMI—a public-private partnership—is funded by The Michael J. Fox Foundation for Parkinson's Research and funding p","journal":"Movement Disorders","year":2025,"id":544460,"datarank":0.0,"base_score":0.0,"endowment":0.0,"self_citation_contribution":0.0,"citation_network_contribution":0.0,"self_endowment_contribution":0.0,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":1,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9575,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2025-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":880088,"name":"Aimee J. Karstens","orcid":"0000-0002-0842-3820","position":1,"is_corresponding":false},{"id":1253899,"name":"Samantha Evy Schoeneman Patel","orcid":"0009-0005-3999-9610","position":2,"is_corresponding":false},{"id":426872,"name":"Jori Fleisher","orcid":"0000-0001-5003-9091","position":3,"is_corresponding":false},{"id":1145279,"name":"Christopher G. Goetz","orcid":"0000-0003-4457-5511","position":4,"is_corresponding":false},{"id":431654,"name":"David Andrés González","orcid":"0000-0003-0882-7689","position":0,"is_corresponding":true}],"reference_count":6,"raw_metadata":null,"created_at":"2026-07-19T02:53:12.864581Z","pmid":"40439012","pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}