A news article reports that researchers have documented a negative correlation between brain size and self-esteem, which leads some readers to conclude that larger brains lead to lower self-esteem. The main problem with this conclusion is that

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The main problem with concluding that larger brains lead to lower self-esteem is that there may be a third variable that is causing both brain size and self-esteem to be related. It is not clear whether larger brains actually cause lower self-esteem, or whether some other factor is causing both brain size and self-esteem to be related in this way. Therefore, the relationship between brain size and self-esteem may not be a causal relationship at all.

A News Article Reports That Researchers Have Documented a Negative