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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
  1. Sukumar Vellakkal1,2,
  2. Christopher Millett1,3,
  3. Sanjay Basu4,5,
  4. Zaky Khan1,
  5. Amina Aitsi-Selmi6,
  6. David Stuckler2,5,
  7. Shah Ebrahim1,7
  1. 1Public Health Foundation of India, New Delhi, India
  2. 2Department of Sociology, Oxford University, Oxford, UK
  3. 3Department of Primary Care and Public Health, Imperial College London, London, UK
  4. 4Prevention Research Center, Stanford University, Stanford, Palo Alto, California, USA
  5. 5Department of Public Health and Policy, London School of Hygiene and Tropical Medicine, London, UK
  6. 6Department of Epidemiology & Public Health, University College London, UK
  7. 7Department of Non-Communicable Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, UK
  1. Correspondence to Dr Sukumar Vellakkal, Public Health Foundation of India, 4 Institutional A, VasantKunj, New Delhi 110070, India; sukumar.vellakkal{at}


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.

  • Epidemiology of chronic non communicable diseases

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