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from the breathe-deeply-and-count-backwards-from-100 dept.
http://www.reuters.com/article/us-health-kids-anesthesia-idUSKBN1322D3
Kids who are exposed to surgical anesthesia before age four tend to have slightly lower school grades at age 16 compared to other kids, but the difference is very small and shouldn't discourage parents from proceeding with necessary surgeries, researchers say.
The "low overall difference in academic performance after childhood exposure to surgery is reassuring," they write in JAMA Pediatrics.
Studying the health and school records of more than 2 million children born in Sweden between 1973 and 1993, the researchers identified 33,000 children who had one surgery with anesthesia before age four and 159,000 children who were similar in most ways but had not had surgery or anesthesia before age 16.
On average, kids who'd had anesthesia had 0.41 percent lower school grades at age 16 and 0.97 percent lower intelligence quotient (IQ) scores at age 18.
Association of Anesthesia and Surgery During Childhood With Long-term Academic Performance (open, DOI: 10.1001/jamapediatrics.2016.3470) (DX)
(Score: 2) by zeigerpuppy on Tuesday November 08 2016, @11:45PM
As to your question of precision of measurement....
You can get an accurate statistical measure of very small differences in a variable of interest (IQ score for instance) as follows.
The individual variability of a test may be a few points (even in the same individual in test-retest). However if you test thousands of individuals and aggregate their scores, their scores will follow a normal distribution (in most cases, also called a bell-curve). Those two groups will have different means to their bell-curves and as you get more data the curves will diverge enough to be statistically different. This difference can be less than individual variability in a measure (as we assume that the individual test-retest variability is also similarly distributed).
They're relatively safe assumptions in this context.
Now the more important question is, "does it matter?"
Well in this case, as you say, the difference is small so it's probably not a big deal but it can still be a real (and small) difference.