Wednesday, March 20, 2013

Placing the de-worming story in its perspective

De-worming has been the poster child of the randomized control trial (RCT) movement in development economics. Its obvious simplicity and cost-effectiveness, apparently validated by numerous RCTs across Asia and Africa, has been highlighted as proof of what evidence-based development policy making can achieve. No serious discussion on evidence-based policy making is today complete without some mention of de-worming. So much so that crusaders are now out to "deworm the world".

In this context, the latest issue of Lancet (pdf here) has some unsettling truths. An RCT of 72 blocks in Uttar Pradesh in India over a period of 5 years, covering over 5000 children in 1-6 year group, conducted by medical scientists, finds that "regular deworming had little effect on child mortality". The randomization was done at the block level, with 4158 ICDS's anganwadi centers in 36 blocks receiving Albendezole tablets twice a year. 

Though the main objective of the study was to explore the effect of de-worming on child mortality, its findings on other physical health parameters carry relevance in light of claims made by RCTs done by economists. The graphic below shows that on a host of physical - height, weight, BMI, haemoglobin level - and illness prevalence parameters, there is no statistically significant difference between the treatment and control groups of children. Furthermore, this finding comes despite the treatment almost halving the prevalence of worm infection. 

Furthermore, the authors compare the physical health parameters between infected and non-infected students within the control group ICDS centers and report similar findings. In fact, for all worm categories, there is no statistically significant difference in health outcomes between the infected and non-infected child populations. 

The main case of the supporters of de-worming is that it prevents students from falling sick frequently and thereby increase their school attendance days. But this study questions the presumption that it contributes to significant health improvements or reduce other disease incidence. Even where worm infection has been halved, it appears to not have contributed to any increase in general physical well-being and lowering of other disease incidence. If this true, how does it square up with the claims of the de-wormers that school attendance increased because of improving child health outcomes and resultant lowering of disease incidence? 

The authors of the study qualify their findings to "lightly infected" areas, which are more likely in rural areas. But this leads us to what is a "high infection" rate? The "de-worming crusaders" themselves report incidence rates at 16% for Delhi slums and 14% for Andhra Pradesh. But this is just half the incidence rate of the "lightly infected" areas in the present study. Other studies of Kathmandu and Assam, two areas one would suspect of being "high incidence", too point to worm infection rates of 10-25%. If this infection range can be generalized across most of developing Asia, then the findings of the present study becomes immediately relevant. 

Now, it is possible for the supporters of de-worming to quibble about the small details of any study and dig their heels in. But what cannot be denied is that contrary to anything they claim, there is no unqualified (or so obviously clear) case for universal and prioritized adoption of de-worming on the highfalutin grounds that it is the most cost-effective intervention to improve student attendance. 

Further, as I have already blogged here, the definition of what constitutes "cost-effectiveness" is certainly flawed. A more appropriate frame of reference for judging "cost-effectiveness" would be the "implementation bandwidth" of public systems. Supporters of de-worming overlook the fact that the limited "implementation bandwidth" of any public system would invariably result in this intervention squeezing the implementation space for all other programs.

None of this is to decry or oppose the idea of de-worming. This is only an attempt to temper the claims around de-worming and locate it in its true perspective. It is a note of caution to the prevailing trend of squeezing the last ounce of "academic juice" from a fairly commonplace intervention. In that sense, this post is deliberately written to be similarly provocative, though in the opposite direction, as the "de-worming crusaders".  

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