'Eighteen' in the Bible

Or do you assume that those eighteen on whom the tower in Siloam fell and killed were worse sinners than all the others who live in Jerusalem?

And there was a woman who for eighteen years had had an illness caused by a spirit (demon). She was bent double, and could not straighten up at all.

And this woman, a daughter (descendant) of Abraham whom Satan has bound for eighteen long years, should she not have been released from this bond on the Sabbath day?”