psychology/ statistics........why we can't say P= 0.000?

Question

why we can't say P= 0.000?

Thank you

Answer 1

Because, assuming you're talking about p-values, p may become pretty darned small but it is never zero. Consider, the normal distribution covers from -infinity to infinity - your statistic may correspond to a point way out in the tail where there is hardly any mass but it ain't zero. Really though, depending on the context a statement like "p<0.0001" or "p<0.00001" is good enough.

Answer 2

P can only equal zero if something is impossible to happen. For example, if you wanted to know the probability of getting 3 heads in 2 coin flips, that would be zero because it is impossible. If you wanted to know the probability of getting 100 heads in 100 coin flips, it is very close to zero but not zero.