Pick One: Sick Kids or Look Poor

Katja is on a roll:

SODIS is a cheap method of disinfecting water by putting it in the sun. Like many things, it works better in physics than society, where its effects were not significant, according to a study in PLoS medicine recently…. [In] Rural Bolivia, where the study was done … the children studied usually get diarrhoea four times a year, which causes about fifteen percent of deaths of children under five. For the poorest quintile in Bolivia the under five death rate is about one in ten of those born alive. … The leader of the study, Daniel Mausezahl, suspects a big reason for this is that lining up water bottles on your roof shows your neighbors that you aren’t rich enough to have more expensive methods of disinfecting water. …

Fascinating as signaling explanations are, this seems incredible. … Perhaps adults are skeptical about effectiveness?  There is apparently good evidence it works though, and there were intensive promotional campaigns during the study. What’s more lack of evidence doesn’t usually stop humans investing in just about anything [medical] that isn’t obviously lethal. …. And parents are known for obsessive interest in their children’s safety. What’s going on?

The study said:

We powered the study to detect a 33% reduction in diarrhoea incidence after reviewing the evidence base for point-of-use water treatment.

So the results are (barely) consistent with the bottles working for everyone who used them, which should reduce kids’s death rate by 1.5%.   Is Katja too accepting of parent propoganda?  When are parents ever willing to make themselves appear poor or low status to reduce their kid’s chance of dying by 1.5%?

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  • bcg

    I’m wondering if on average, after factoring in the consequences of looking poor, the parents who risk it come out ahead.

  • jonathan

    Study notes several reasons why it didn’t work without getting into public display issues – which may have been seen as a positive in this circumstance.

    “First, the estimate for the longitudinal prevalence of diarrhoea was substantially smaller (OR = 0.92, 95% CI 0.66–1.29) than the estimate for incidence and there is some evidence that prevalence is a better predictor in terms of mortality and weight gain than incidence [23]. The absence of a time-intervention interaction in our time-dependent analysis suggested no increased health benefits with the ongoing intervention. Furthermore, within the intervention arm, there was no evidence that increased compliance was associated with a lower incidence of diarrhoea (Figure 4). However, we interpret this post hoc subgroup analysis cautiously because compliant SODIS users might differ in important ways from noncompliant users. A compliant SODIS user might be more accurately keeping morbidity diaries, whereas less compliant families may tend to underreport diarrhoeal illness. Or, households with a high burden of morbidity might be more likely to be compliant with the intervention. Both of these scenarios could lead to an underestimation of the effectiveness of SODIS.

    In our study the lack of blinding may have reduced motivation in the control communities. However, the number of households lost during follow-up and the number of days under observation were almost identical in both arms. Additionally, the control communities knew that they would receive the intervention after study end. Finally, a reduction of diarrhoea frequency of 20% might be insufficient to be well perceived, i.e., have a noticeable impact in a population with a high burden of child diarrhoea and will, thus, not result in a sustainable behavioural change. Faecal contamination in about 60% of the yards indicates a highly contaminated environment with presumably a large potential for transmission pathways other than consuming contaminated water. This simultaneous exposure to a multiplicity of transmission pathways may explain why we found no significant diarrhoea reduction due to SODIS.”

  • Robert

    At this rate Katja will be a co-blogger here in no time 🙂

  • Ultraviolet light is well known to be a good disinfectant. Unfortunately, glass is also well known to block UV light. Has anyone actually studied whether the water in the bottles is really getting noticeably disinfected?

    • david

      Yes, that’s why SODIS instructions specify the use of PET (polyethylene terephthalate) bottles. Polycarbonate, PVC and glass bottles all block UV light and are not recommended.

      The water is indeed getting disinfected, here are studies.

      • Curt Adams

        I see a real problem with a technique that requires illiterate peasants to be able to reliably distinguish between polyethylene terephthalate and polyvinyl chloride because of differential UV opacity – even though there eyes tell them both are clear as can be.

        Hauling all the water you drink onto the roof effectively the day before you use it (you need six hours of full sun) is a pretty substantial inconvenience as well. I also wonder about the psychological effect – people generally associate cleanliness with elaborate rituals rather than absence of germs (which, of course, humans can’t detect without substantial technological assistance). Leaving something lying around doesn’t seem like a way to get it clean, regardless of whether it is (and, again, expecting illiterate peasants to understand photochemical microbiology well enough to overcome natural instincts isn’t realistic). Maybe a mirrored sun-concentrating “sterilization box” would get better use.

  • Jess Riedel

    Minor: I think the word “improve” needs to be removed from the last sentence in the post.

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  • david

    Some other hypotheses:

    Using SODIS signals your lack of trust in the municipal water supply in a very public way. Control over said supply is often in the hands of local political elites. Two and two together…

    Poor communities in tropical nations often use water to cool off. Water in the sun is hot. One could move the bottles to storage, but it’ll take a long time to cool to the level of groundwater or tapwater, and will multiply the costs of SODIS (more bottles, and more effort).

    When one is thirsty, one’s in a hurry. Drinking from wherever may be easier than tracking down the nearest treated bottle.

    The process of SODIS is actually rather involved, involving filtering if the water is turbid, collecting and cleaning bottles, refilling etc. It’s not just leaving bottles in the sun. This can be time-consuming, which itself directly burns income that might be otherwise used for education or food, both of which are also useful.

    Bottles left in the sun are easily stolen. Maybe such bottles should be modeled as a public good? Underprovision?

  • Doug S.
  • I’ve seen this technique discussed before, and it’s very promising. If there’s physics proof-of-principle, but if there’s a disconnect in the actual results, the smart money is on poor compliance. Think about how non-compliant patients are with medicine right here in the U.S. when it’s in their own self-interest. People on anti-hypertensives are some of the worst. First, they lie and say they’re taking them. Or, they take them half-ass when they remember to. They think “I don’t feel sick, so I don’t need to take these.” When they get caught they say nonsensical things to their docs like “I don’t want to become dependent on it.” These are well-educated people supposedly acting in their own self-interest, and we’re surprised that illiterate people would (perhaps out of status signalling) not comply with the program, and then lie to researchers about it that they did?

    Whether it’s physics or irrational people that’s the problem, the bottom line is the technique is useless if you can’t get them to actually do it (just like a drug that’s so troublesome that people don’t take it the way it’s supposed to be taken). Yes, people the world over are obsessed with their kids’ safety, but in many places that still means praying a certain number of times a day, rather than listening to what the medical people from the NGO tell you.

  • tim

    I spent some time in rural Bolivia this year and these results don’t surprise me. Bolivians inhabit a very stratified society and systematic classification is enforced most by those who have very little. I would argue with Curt whether this is down to “illiterate peasants” who don’t understand hygiene, though. Despite rampant poverty and superstition, the country is not so very divorced from the modern Western world. I met some surprisingly sophisticated people in very rural environs, including no small number of poor kids who saved their bolivianos to play World of WarCraft in internet cafes.

  • Yvain

    How about just normal human inability to deal with small probabilities, and normal human reluctance to accept something is working when there’s no direct evidence?

    Compare this to medication non-compliance in Western countries. Some studies show statin compliance at around 50% after six months. People aren’t good at taking a medication when there’s no way to know it’s having effects, and when the effects are on the order of a few percent shift in the incidence of certain diseases they may never have heard of. You wouldn’t immediately conclude from the statin non-compliance that people don’t really care if they get heart attacks or not. And that’s even without the potential status hit.

    To test this theory versus the theory that parents care more about status than about their kids’ survival, you’d need to reverse the situation and find an action that could be taken to prevent a small and untraceable chance of future status loss, but which had obvious and significant detrimental effects on the health of children. I can’t think of any such action right now, but I predict that if someone can think of one, parents will be very reluctant to do it.

  • This implies that your evidence for healthcare not working is weaker than it seems. If people are not willing to accept obviously superior health in exchange for a slight ding on social status, then the fact that they don’t value healthcare (for example in your hospital-shopping post) doesn’t prove that healthcare doesn’t do anything.

  • John Maxwell IV

    Consider how many people in Western countries don’t exercise regularly even when there’s an overwhelming and well-known medical consensus that exercise is a Good Thing.

    For whatever reason, it seems that people rarely follow good advice unless it applies in a domain they’ve been thinking about.

  • Mario Cruz

    Have no hard evidence, I’ve just heard that Bolivians don’t eat anything made out of corn, becuase corn is food for animals. Anyone eating corn is seen as not rich enough to buy more expensive nutrition agents so they rather stay undernourished (something similar happens with water, see a trend there). Corn has played a major role in many succesful societies that had no cultural bias towards corn. Even european inmigrants that settled from Texas to California found in corn one a way to adapt to their new environment (see corn bread wide use in southwest cuisine).

    Saludos desde México!


    • tim

      I’m interested to know where you heard that, because there’s no truth to it. Corn is enjoyed by Bolivians regardless of status. Corn on the cob is sold roadside in rural areas and corn is often an ingredient in traditional soups. Cebiche is pretty popular in Bolivia as well, and it’s usually served with sweet corn. Corn is probably second only to potatoes as a staple in Bolivia. Espero que esto es informativo.

  • This is one of my all-time favorite posts (and most horrifying facts) on Overcoming Bias. It has convinced me that money is only a proxy: Status makes the world go ’round.

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