Question 4: Why did the the authors NOT conclude that that breast feeding has no effect on intelligence in children.
The difference is not significant, so we cannot conclude that there is an effect. This may be because there is no effect, or it may be that the effect is simply too small for our sample to detect. We may have made a Type II error, failing to detect a difference in the population. We cannot tell which of these is the case, null hypothesis true or Type II error.
We should never conclude that there is no effect.
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