Bad Stuff in Food: Risk Analysis and Political Commentary: Individual Choice

Public Health Value Judgments

When you can’t have it all, which is pretty much all the time, it is necessary to set priorities. Other people (e.g. friends, relations, employers, and the government) are often there to help you set your priorities – whether you want them to or not. But still, everybody does have to make their own choices on occasion. For example, unless your mom, spouse, or religion chime in, you can choose what fish you eat and how much all by yourself. You probably already know whether you like fish or not, and you also probably know how much it costs. If there are other factors that go into the decision, then you will need to know what they are.

Unfortunately, the trend in public health these days is give consumers food consumption advice without exactly saying why. There is no good reason for this that I know of, but I am aware of two of the bad ones. First, not getting in to the gritty details avoids political controversy stemming from scientific uncertainties. That doesn’t mean the advice in necessarily bad, but then again maybe it is. Second, doling out public advice can be a career all by itself, and career advisers often care more about protecting their jobs than whether or not the advice is sensible. So, at best, food consumption advice is an expression of the social values of the people giving advice - which may or may not correspond to your values. At worst, the advice doesn’t reflect anyone’s valuation at all. As a result, distrusting public health advice is generally a pretty good idea, especially when the advice isn’t accompanied by some intelligible reasons for it, which will also permit you decide for yourself if those reasons are good enough for you.

Grading on the Curve

While psychology studies are sometimes grounded in physiology with physical measurements (e.g. nerve conduction velocity), most epidemiological studies concerned with neurobehavioral development largely employ batteries of tests that reflect the social science interface of psychology. Since the value of these tests is subjective, they are standardized by determining how subjects “normally” perform. Since variation in performance on tests is normal, the tests are typically given numerical values that reflect how far above or below average a score is relative to much it normally varies. There are a two major problems with this. First, how much a test score varies isn’t necessarily a good indicator of how much performance on the test really matters. Second, defining what a “normal” population can be rather arbitrary. For example, the Denver Developmental Screening Test was originally standardized in Denver, while the Boston Naming Test was developed in Boston. Yet, what is normal in Denver may be somewhat different from what is normal in Boston. For a book length discussion of the problems with standardized testing, see Gould (1981). Nonetheless, standardized psychological test batteries are more objective and reproducible than a doctor’s or a teacher’s opinion, and they are widely used for that reason.

The most basic normalized scale used for psychological testing is the Z-score where the difference between the average and test score is divided by the standard deviation. As a result, a -1 signifies a test result that is one standard deviation below the average, while a value of +1 signifies a test result that is one standard deviation above average. Other standardized tests are often scaled with modified with modified Z-scores. In particular, the Intelligence Quotient (IQ) is scaled with a mean is defined to be 100 and the standard deviation is 15, while Scholastic Aptitude Tests (SAT) have a mean of 500 and a standard deviation of 100. The following table compares how test results are scaled with each method:

	2 SD below	1 SD below	Average	1 SD above	2 SD above
Z-Score	-2	-1	0	1	2
IQ	70	85	100	115	130
SAT	300	400	500	600	700

Individual Neurobehavioral Risks and Benefits Arising From Fish Consumption

So, let’s talk about fish. The point of the preceding discussion is that there is evidence that the consumption of fish during pregnancy may have both bad (from methylmercury) and good (from omega-3 fatty acids or perhaps something else) effects on future neurobehavioral performance of the child – and the effects aren’t exactly the same. Plus, I’m not going to tell you what you should do. I am leaving that to be your problem, and since it really isn’t a simple decision I have no idea what you will decide. However, I will do my best to supply some reliable information.

My main vehicle for information delivery is an Excel-based program, which is a slightly modified version of a risk-benefit assessment model that I developed while I was at the FDA (2014). Although there are some other minor modifications as well, the main difference is that this version of the model is intended to estimate risks for a specific individual. However, if you don’t have Excel, or it is more trouble than it is worth, here are some sample results that give a feel for what the program does:

Consuming a high mercury such as swordfish fish twice a week during pregnancy will result in a developmental delay of the age at which a toddler learns to walk of about a week. The uncertainty associated with this estimate ranges from 0 to about three weeks.
Consuming one can of albacore tuna and one can of albacore tuna once a week during pregnancy will result in an increase of about 2.5 IQ points in the child. However, there may be a decrement in IQ of about 0.3 points, or the increase may be as much as 3.5 points.
Consuming salmon once a week will result in a projected increase in performance on the Verbal SAT of about 25 points. However, given the many uncertainties association wit the estimate, the increase may be as little as 0 or as much as 35 points.