Another Important Inadvertent Experiment

Immigrants arriving in Sweden were allocated to high, medium or low poverty areas by immigration officers who had minimal information about the immigrant, and no personal contact.[1] Adjustment could be performed for such small differences as existed at baseline in educational level, time of arrival in Sweden, and so on. The study showed that allocation to a high-income area was associated with lower diabetes risk, and the relative risk advantage increased progressively with duration of ‘exposure’. This study, of over 64,000 people, is one of the first semi-experimental studies to test for ‘neighbourhood effects’. A somewhat similar study in the USA was based on actual randomisation of poor people to move to higher income areas or remain where they were.[2] This study showed lower obesity and levels of glycated haemoglobin (HbA1c) in those randomised to move, providing further experimental evidence for neighbourhood effects (see previous item).

— Richard Lilford, CLAHRC WM Director


  1. White JS, Hamad R, Li X, et al. Long-term effects of neighbourhood deprivation on diabetes risk: quasi-experimental evidence from a refugee dispersal policy in Sweden. Lancet Diabetes Endocrinol. 2016; 4(6): 517-24.
  2. Ludwig J, Sanbonmatsu L, Gennetian L, et al. Neighbourhoods, Obesity and Diabetes – A Randomized Social Experiment. N Engl J Med. 2011; 365: 1509-19.

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