Estatística
It must be emphasized that statistical hypotheses are to be stated before data are collected to test them. To propose hypotheses after examination of data can invalidate a statistical test. One may, however, legitimately formulate hypotheses after inspecting data if a new set of data is then collected with which to test the hypotheses.
Livro: Biostatistical Analysis (Third Edition)
Autor: Jerrold H. Zar
Página: 79