...'entire population'?
Alright, I have to admit I have no idea what test you are now referring to. I thought we were discussing the Pygmalion results in which a small sample of elementary school students turned in increased IQ scores, which could be explained by a number of well-known and perfectly ordinary processes.
But it seems like you're talking about something completely else and may be thinking of country-level Flynn effects or something, I have no idea what.
The PitC study showed an 8 point IQ increase in the control group. You offered those three explanations and said that they explained why that wasn't particularly unusual, and my understanding of normed IQ tests is that they are expected to remain constant over short times.
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