Unpicking global health statistics

Posted on 07/11/2015 by Fiona Gore (WHO) and Tim Brewer (WaterAid)


Decision-makers need to know who’s dying of what, where and why, if they are to make recommendations for action. Unfortunately, disease estimates may vary due to different methods being applied and new data becoming available. 

Occasionally, different estimates have been at the centre of intense debates. For example, the Lancet has published health statistics on WASH, which on some issues differed substantively from WHO figures

So how should a decision-maker at country level make sense of two mortality estimates for the same risk factor? Use of increasingly complex methods add to any confusion and may lead to good research being under-used, not shared, or simply put aside.

To better make sense of the figures, I am proposing below an “idiot’s guide” to WASH-related health statistics. We have made it simple by quoting only one source for each figure. 


What is the health impact of lack of basic water, sanitation and hygiene services (e.g. wells and pit latrines)? What about safely managed services (e.g. taps and toilets)?

  • A new WHO estimate attributes 58% of global diarrhoea burden to the lack of basic water, sanitation and hygiene services.

What’s that in real numbers?

  • 842,000 people per year die of diarrhoea because of lack of basic WASH.


Are other diseases also related to lack of WASH? Does safer water still mean better health?

  • Yes! Around 50% of malnutrition is estimated to be basic WASH related (as people cannot retain the nutrients they take in), and this contributes to a range of other diseases.
  • The majority of Neglected Tropical Diseases (NTDs) are related to lack of basic WASH.
  • Around 23% of Pneumonia, which is the leading killer of children in the world, is basic WASH related.
  • Neo-natal mortality and maternal mortality, particularly from sepsis, are highly likely to be related to lack of safely managed WASH in birth settings (really, some people have built hospitals without taps or toilets).
  • Hospital-acquired infections are spread through poor hygiene in the UK, so in health centres without safely managed water or sanitation we can only imagine the effect (really - there’s almost no data on this).


So if we add up all the people who die of malnutrition, NTDs, Pneumonia and Diarrhoea, and divide by those percentages, we get the WASH impact?

  • Unfortunately, no. These various illnesses overlap and records of the disease burden are poor in poor countries.
  • Statistical modeling can help take this complexity into account, but the results are very sensitive to the starting ‘facts’ (which may be based on limited data) and the specific methods used (which may be flawed), so often these estimates are contested within the academic community. This is inconvenient for policy makers, though necessary for truth.


  • The most recent estimate for the burden of diseases attributable to unsafe WASH, taking the best available facts and the latest magic, sorry, statistical models, comes from the Institute for Health Metrics Global Burden of Disease Study Comparative Risk Analysis.


What does that say?

  • 1.4 million people died from illnesses related to lack of safely managed WASH in 2015.
  • As far as we can tell, in Africa lack of safely managed WASH is the third biggest cause of disease.
  • But! This still doesn’t include all the health impacts, or the role of WASH beyond the household (e.g. health centres or in schools) in the disease burden.
  • And it remains unclear what the net benefit would be if we could reach all people with at least basic water, sanitation and hygiene (a more achievable short-term goal for the poorest people).


So if basic WASH related diarrhoea is 842,000, and all disease deaths related to safely managed WASH services are at least 1.4 million, then WASH related non-diarrhoeal disease is 558,000!

  • No! The story remains complex and simple math cannot provide the answer. With global health statistics, you can’t have pick-n-mix magic. 


Your comments (1)

Megan Wilson-Jones, WaterAid UK, 16/03/2016

Really interesting blog and so useful to have all the stats laid out in one place! To expand on the links between WASH and nutrition, its important to remember that the pathways are complex and multifaceted. Poor WASH contributes to undernutrition through three key pathways which impact on the way in which nutrients are retained and absorbed in the body. The direct pathways include 1) diarrhoea - it has been estimated that a quarter of stunting can be attributed to 5 or more episodes of diarrhoea in the first 2 years of life; 2) Intestinal worms - these infections are transmitted via contact with or ingestion of soil contaminated with faeces containing worm eggs, and can lead to anaemia and poor growth; and 3) Environmental Enteric Dysfunction (EED) a sub-clinical condition in which the structure and function of the intestine is damaged, hindering the absorption of nutrients. There are also various other indirect links such as time to fetch water and cost of water, which can impact on the care of young children.

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