To call in the statistician after the experiment is done may be no more than asking him to perform a post-mortem examination: he may be able to say what the experiment died of.

Natural selection is a mechanism for generating an exceedingly high degree of improbability.

... the actual and physical conduct of an experiment must govern the statistical procedure of its interpretation.

If ... we choose a group of social phenomena with no antecedent knowledge of the causation or absence of causation among them, then the calculation of correlation coefficients, total or partial, will not advance us a step toward evaluating the importance of the causes at work.