title: A statistical analysis of 'rule-out' diagnoses in outpatient health insurance claims in Japan.
abstract: BACKGROUND
  As each clinical procedure must be justified by a corresponding diagnosis in Japanese health insurance claim (HIC), unconfirmed diagnoses marked as rule-out diagnoses will be written on an HIC. However, little is known about the statistical profiles of such rule-out diagnoses.
  
  
  OBJECTIVE
  To illustrate the basic statistical profiles of rule-out diagnoses.
  
  
  METHODS
  We analysed all the diagnoses on 169 622 outpatient HICs in May 2006 from corporate health insurance societies. The proportions of additional diagnoses and rule-out diagnoses in each of the major disease categories defined by the Classification of Diseases for the use of Social Insurance, which is based on the International Statistical Classification of Diseases and Related Health Problems 10th Revision were calculated.
  
  
  RESULTS
  There were 442 010 diagnoses on the HICs, of which 96 253 (21.8%) were principal diagnoses and 345 757 (78.2%) were additional diagnoses. Of the principal diagnoses, 1022 (1.1%) were rule-out diagnoses. Of the additional diagnoses, 19 308 (5.6%) were rule-out diagnoses. The percentage of rule-out diagnoses in the additional diagnosis category was significantly higher than that in the principal diagnosis category. Among the major disease categories, neoplasms showed the highest percentage of rule-out diagnoses for both principal diagnosis and additional diagnosis.
  
  
  CONCLUSIONS
  The existence of rule-out diagnoses affects the results of statistics based on HIC data. Japanese statistics based on HIC data should be improved by utilizing the information on rule-out diagnoses.
authors.affiliation: Department of Hygiene and Preventive Medicine, School of Medicine, Fukuoka University, Fukuoka, Japan. taniyan@fukuoka-u.ac.jp
authors.forename: Shinichi
authors.initials: S
authors.lastname: Tanihara
authors.forename: Etsuji
authors.initials: E
authors.lastname: Okamoto
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Une
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D002648:Child; D002675:Child, Preschool; D015897:Comorbidity; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007345:Insurance Claim Review / Q000706:statistics & numerical data*; D007348:Insurance, Health / Q000706:statistics & numerical data*; D007564:Japan; D008297:Male; D008875:Middle Aged; D010045:Outpatients / Q000706:statistics & numerical data*; D017678:Sex Distribution; D055815:Young Adult