A major health study indicated that there's a birth month effect for schizophrenia. If a child is born during a certain month, he or she has a significantly higher chance of developing schizophrenia later in life, however, the chance of developing schizophrenia only increases by 1 in 10 million.

Based on common knowledge about t-tests, how can there be a significant difference for that particular month when there's such a small increase in the chances of developing schizophrenia?

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