title: Screening for asthma by population ranking: a validation study.
abstract: OBJECTIVE
  A neural network system was previously developed to rank a population in order of asthma probability based on responses to a postal questionnaire. Respondents ranked higher than a percentage point screening threshold are offered clinical review. The present study validates this system in a new population that had not been involved in system development.
  
  
  METHODS
  The system was used to rank respondents to a community survey and to predict positive predictive value (PPV) for percentage point thresholds between the top 1% and 10% of the ranking. Respondents in the top 10% were invited for clinical review. Review information and expert opinion was used to designate respondents as clinically "asthmatic" or "non-asthmatic." PPV prediction for each threshold was compared with clinical status of respondents.
  
  
  RESULTS
  As the threshold increased from 1% to 10%, the additional yield of clinical asthmatics decreased, indicating a ranking in asthma probability order (all 7 in the top 1% were clinical asthmatics compared with 91% of the top 5% and 83% of the top 10%). Percentages of clinical asthmatics were generally slightly higher than system PPV predictions.
  
  
  CONCLUSIONS
  The system ranked the population in asthma probability order and estimated PPV conservatively, enabling health-care providers to predict resource implications of a screening program.
authors.affiliation: General Practice Research Unit, North West Lung Research Centre, Wythenshawe Hospital, Manchester, M23 9LT, UK. sybil@miga.demon.co.uk
authors.forename: Sybil
authors.initials: S
authors.lastname: Hirsch
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Frank
authors.forename: Michelle
authors.initials: M
authors.lastname: Hazell
authors.forename: Peter I
authors.initials: PI
authors.lastname: Frank
mesh_terms: D001249:Asthma / Q000453:epidemiology*; D006801:Humans; D008433:Mathematics; D016571:Neural Networks, Computer; D011795:Surveys and Questionnaires