title: A novel approach used outcome distribution curves to estimate the population-level impact of a public health intervention.
abstract: OBJECTIVE
  To provide an analytical framework within which public health interventions can be evaluated, present its mathematical proof, and demonstrate its use using real trial data.
  
  
  METHODS
  This article describes a method to assess population-level effects by describing change using the distribution curve. The area between the two overlapping distribution curves at baseline and follow-up represents the impact of the intervention, that is, the proportion of the target population that benefited from the intervention.
  
  
  RESULTS
  Using trial data from a parenting program, empirical proof of the idea is demonstrated on a measure of behavioral problems in 355 preschoolers using the Gaussian distribution curve. The intervention group had a 12% [9%-17%] health gain, whereas the control group had 3% [1%-7%]. In addition, for the subgroup of parents with lower education, the intervention produced a 15% [6%-25%] improvement, whereas for the group of parents with higher education the net health gain was 6% [4%-16%].
  
  
  CONCLUSIONS
  It is possible to calculate the impact of public health interventions by using the distribution curve of a variable, which requires knowing the distribution function. The method can be used to assess the differential impact of population interventions and their potential to improve health inequities.
authors.affiliation: Department of Women's and Children's Health, Uppsala University, 751 85 Uppsala, Sweden. Electronic address: Anna.Sarkadi@kbh.uu.se.
authors.forename: Anna
authors.initials: A
authors.lastname: Sarkadi
authors.affiliation: Department of Women's and Children's Health, Uppsala University, 751 85 Uppsala, Sweden.
authors.forename: Filipa
authors.initials: F
authors.lastname: Sampaio
authors.affiliation: National Institute of Health and Care Excellence, Centre for Public Health, London, SW1A 2BU UK; Institute of Public Health, General Practice and Primary Care Research Unit, University of Cambridge, Cambridge, CB2 0SR UK.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Kelly
authors.affiliation: Department of Women's and Children's Health, Uppsala University, 751 85 Uppsala, Sweden.
authors.forename: Inna
authors.initials: I
authors.lastname: Feldman
mesh_terms: D000328:Adult; D002675:Child, Preschool; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D008297:Male; D017063:Outcome Assessment, Health Care / Q000379:methods / Q000592:standards; D010290:Parents / Q000193:education; D011634:Public Health / Q000379:methods* / Q000592:standards*; D015980:Public Health Practice / Q000592:standards
keywords: Area under the curve; Intervention studies; Normal distribution; Parenting education; Primary prevention; Public health