抄録
It is impossible to get geological data randomly. Nevertheless, many significant suggestions are given by the data analysis based on a textbook of statistic procedure, if it is used carefully. There is another point that we must pay attention to. An usual textbook states how we avoid to conclude that the means of two populations having an equal mean value are different, but does not state the procedure to avoid the opposite error. If we forget these points, the statistical analysis gives us wrong conclusions.
