Sunday, October 26, 2014

Spina bifida and GMOs

One of the claims made by SHAKA is that rates of spina bifida on Maui and Kauai are double the national average, and they suspect GMOs as the cause. This suspicion is entirely imaginary, as no one knows what causes this neural tube deformation; and no mechanism between GMO farming and the disease is proposed.

But is it even true that rates of spina bifida are double the national average? Let’s see.

Spina bifida is a reportable disease, so we know that there are about 8 cases a year in Hawaii, and perhaps others that are not reported because the fetus is aborted. The defect ranges from mild to severe and sometimes takes some time after birth to be noticed.

A known risk factor is insufficient folic acid in the mother’s diet during pregnancy, and about 3 in 5 Maui mothers do not get enough. However, there are 1,800 births a year on Maui and there are not 1,100 cases of spina bifida -- as we will see, the incidence is around 1 or less -- so rather than thinking of folic acid as a preventive, perhaps it would be better to think of it as something that interferes with the developmental failure in the rare cases when that is imminent.

Spina bifida has been around since long before gene splicing, so -- even if there is  a new cause at work today -- there must also be a background rate. Let us assign that as 1 per county per year. We will disregard the fact that 3 in 4 births are on Oahu, and treat each county as equal.

That leaves 4 cases a year that might be outside the base rate. Since SHAKA claims both Maui and Kauai are implicated, then the maximum number of anomalous cases is 2 on Maui and 2 on Kauai.

By making the unrealistic assumption that most cases of spina bifida occur outside Oahu, it is just barely arithmetically possible to claim that rates on Maui and Kauai could   be double the national average. But If the base rate for the Neighbor Islands is 1 per county per year, and if three-quarters of base cases occur on Oahu, there are not any available Neighbor Islands cases to be anomalous. We would need more than 8 total cases to make the sums work. (We require 12 cases to reach baseline.)

So, whatever the base rate is on Maui, it must be less than 1 per year.

Now we run into what might be called the Tyranny of Small Numbers. Let’s say you have 4 instances -- it might be 4 cases of spina bifida on Maui and Kauai attributable to GMOs. They can divide (between counties) as 4/0, 3/1, 2/2, 1/3 or 0/4.

And like every other natural phenomenon, they will. Think of hurricanes in Florida. Over a long period, the number coming ashore is about 1 per year. But there have been years with 4, and for the last 8 years or so, not any. Not just not any per year; not any over that longish period.

So let’s say you know (although you don’t) what the base or natural rate of spina bifida is on Maui. Let’s say it is 1. Let’s say in a year you have 4 total cases.

You cannot call these anomalous, because if the natural average rate is 1, then in some years you will have 4 natural cases, and in other years 0.

You would need a long series of years to know if you had a trend.

So, like all the other SHAKA claims I have checked, this one is bogus. (The only way to make it not bogus would be to claim a huge spike in cases; claiming a mere doubling won’t do it, it just shows they are making things up -- and don’t understand evidentiary rules.)

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