title: Rasch analysis for assessing unidimensionality and identifying measurement biases of malignancy scores in oncology. The example of the Weiss histopathological system for the diagnosis of adrenocortical cancer.
abstract: OBJECTIVE
  Many malignancy scores have been developed without comprehensive statistical or measurement validation, and in particular without verification of the necessary property of unidimensionality. Here, we used Rasch analysis to assess unidimensionality and identify measurement biases of malignancy scores.
  
  
  METHODS
  The Weiss histopathological system (WHS), summing nine items of histopathological alteration, was used to evaluate 247 adrenocortical tumors. Rasch model analysis was implemented and compared to classical factor analytic methods to investigate the validity of item-score summation for both the original and modified WHS, to assess differential functioning of the WHS items across various factors related to patient and tumors, and to identify items or subtypes of tumors that could be considered for removal or exclusion from the WHS with the aims of improving measurement and relieving the burden on pathologists.
  
  
  RESULTS
  The WHS does not meet the necessary property of unidimensionality and is severely affected by differential item functioning in relation to size and weight of the tumor. Moreover, items are not well distributed along the spectrum of malignancy, most being located in the upper part and several at the same place.
  
  
  CONCLUSIONS
  The WHS in its present form should be applied only to small or moderate size tumors, and better scoring systems could be developed by using more appropriately distributed items. Rasch analysis is a powerful method for developing, evaluating, refining and simplifying malignancy scores.
authors.affiliation: Biostatistics and Epidemiology Unit, Assistance Publique-Hôpitaux de Paris, Hôtel Dieu, Paris, France; Research unit APEMAC, EA 4360, Lorraine Université, Université Paris-Descartes, Paris, France. Electronic address: joel.coste@htd.aphp.fr.
authors.forename: Joël
authors.initials: J
authors.lastname: Coste
authors.affiliation: Department of Pathology, Assistance Publique-Hôpitaux de Paris, Hôpital de la Pitié Salpétrière, Pierre et Marie Curie University, Sorbonne Universities, Paris, France; Department of Pathology, Assistance Publique-Hôpitaux de Paris, Hôpital Cochin, Université Paris-Descartes, Paris, France.
authors.forename: Frédérique
authors.initials: F
authors.lastname: Tissier
authors.affiliation: Biostatistics and Epidemiology Unit, Assistance Publique-Hôpitaux de Paris, Hôtel Dieu, Paris, France; Research unit APEMAC, EA 4360, Lorraine Université, Université Paris-Descartes, Paris, France.
authors.forename: Jacques
authors.initials: J
authors.lastname: Pouchot
authors.affiliation: Research unit APEMAC, EA 4360, Lorraine Université, Université Paris-Descartes, Paris, France.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Ecosse
authors.affiliation: Biostatistics and Epidemiology Unit, Assistance Publique-Hôpitaux de Paris, Hôtel Dieu, Paris, France.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Rouquette
authors.affiliation: Department of Endocrinology, Center for Rare Adrenal Diseases, Assistance Publique-Hôpitaux de Paris, Hôpital Cochin, Université Paris-Descartes, Paris, France.
authors.forename: Xavier
authors.initials: X
authors.lastname: Bertagna
authors.affiliation: Department of Endocrinology, Center for Rare Adrenal Diseases, Assistance Publique-Hôpitaux de Paris, Hôpital Cochin, Université Paris-Descartes, Paris, France.
authors.forename: Rossella
authors.initials: R
authors.lastname: Libé
authors.affiliation: Biostatistics and Epidemiology Unit, Assistance Publique-Hôpitaux de Paris, Hôtel Dieu, Paris, France.
authors.forename: Vivian
authors.initials: V
authors.lastname: Viallon
mesh_terms: D000306:Adrenal Cortex Neoplasms / Q000175:diagnosis* / Q000473:pathology*; D000328:Adult; D015982:Bias; D005260:Female; D006801:Humans; D008297:Male; D008495:Medical Oncology / Q000379:methods*; D008875:Middle Aged; D017063:Outcome Assessment, Health Care / Q000379:methods*; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires
keywords: Malignancy scores; Measurement biases; Rasch model analysis; Unidimensionality; Weiss histopathological system