The "rule of 3" is for zero numerators only; the rule of 3,5,7,9,10 is for numerators up to 4.
Mathematically, numerators almost equal to denominators have the same problems as very small numerators, so ( as discussed in lecture and examples in the text) these rules can also be used to get lower limits of 95% CI when the numerator is almost = to or = to the denominator.
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