title: Are estimates of socioeconomic inequalities in chronic disease artefactually narrowed by self-reported measures of prevalence in low-income and middle-income countries? Findings from the WHO-SAGE survey.
abstract: BACKGROUND
  The use of self-reported measures of chronic disease may substantially underestimate prevalence in low-income and middle-income country settings, especially in groups with lower socioeconomic status (SES). We sought to determine whether socioeconomic inequalities in the prevalence of non-communicable chronic diseases (NCDs) differ if estimated by using symptom-based or criterion-based measures compared with self-reported physician diagnoses.
  
  
  METHODS
  Using population-representative data sets of the WHO Study of Global Ageing and Adult Health (SAGE), 2007-2010 (n=42 464), we calculated wealth-related and education-related concentration indices of self-reported diagnoses and symptom-based measures of angina, hypertension, asthma/chronic lung disease, visual impairment and depression in three 'low-income and lower middle-income countries'-China, Ghana and India-and three 'upper-middle-income countries'-Mexico, Russia and South Africa.
  
  
  RESULTS
  SES gradients in NCD prevalence tended to be positive for self-reported diagnoses compared with symptom-based/criterion-based measures. In China, Ghana and India, SES gradients were positive for hypertension, angina, visual impairment and depression when using self-reported diagnoses, but were attenuated or became negative when using symptom-based/criterion-based measures. In Mexico, Russia and South Africa, this distinction was not observed consistently. For example, concentration index of self-reported versus symptom-based angina were: in China: 0.07 vs. -0.11, Ghana: 0.04 vs. -0.21, India: 0.02 vs. -0.16, Mexico: 0.19 vs. -0.22, Russia: -0.01 vs. -0.02 and South Africa: 0.37 vs. 0.02.
  
  
  CONCLUSIONS
  Socioeconomic inequalities in NCD prevalence tend to be artefactually positive when using self-report compared with symptom-based or criterion-based diagnostic criteria, with greater bias occurring in low-income countries. Using standardised, symptom-based measures would provide more valid estimates of NCD inequalities.
authors.affiliation: Public Health Foundation of India, New Delhi, India Department of Sociology, Oxford University, Oxford, UK.
authors.forename: Sukumar
authors.initials: S
authors.lastname: Vellakkal
authors.affiliation: Public Health Foundation of India, New Delhi, India Department of Primary Care and Public Health, Imperial College London, London, UK.
authors.forename: Christopher
authors.initials: C
authors.lastname: Millett
authors.affiliation: Prevention Research Center, Stanford University, Stanford, Palo Alto, California, USA Department of Public Health and Policy, London School of Hygiene and Tropical Medicine, London, UK.
authors.forename: Sanjay
authors.initials: S
authors.lastname: Basu
authors.affiliation: Public Health Foundation of India, New Delhi, India.
authors.forename: Zaky
authors.initials: Z
authors.lastname: Khan
authors.affiliation: Department of Epidemiology & Public Health, University College London, UK.
authors.forename: Amina
authors.initials: A
authors.lastname: Aitsi-Selmi
authors.affiliation: Department of Sociology, Oxford University, Oxford, UK Department of Public Health and Policy, London School of Hygiene and Tropical Medicine, London, UK.
authors.forename: David
authors.initials: D
authors.lastname: Stuckler
authors.affiliation: Public Health Foundation of India, New Delhi, India Department of Non-Communicable Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, UK.
authors.forename: Shah
authors.initials: S
authors.lastname: Ebrahim
mesh_terms: D000293:Adolescent; D000328:Adult; D015982:Bias; D002908:Chronic Disease / Q000191:economics / Q000453:epidemiology*; D019049:Developed Countries / Q000191:economics / Q000706:statistics & numerical data*; D003906:Developing Countries / Q000191:economics / Q000706:statistics & numerical data*; D004522:Educational Status; D005260:Female; D006306:Health Surveys; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D057566:Self Report; D017678:Sex Distribution; D012923:Social Class; D014944:World Health Organization; D055815:Young Adult
keywords: Epidemiology of chronic non communicable diseases; INEQUALITIES; PUBLIC HEALTH