Abstract: Up and down method was originally devised for sensitivity testing by W.J. Dixon and A.M. Mood and developed by some other experts, but all these traditional up and down methods can not use previous data effectively, and, besides, the estimates for variance are not exact. This paper establishes a two dimensional up and down method which is applicable for small samples and can be used for estimating percentiles and percentages of sensitivity variables by combining previous experimential data and current test data, and furthermore, gives the confidence limits of the percentiles and percentages. The information that can be used in the two dimensional up and down method is much more than that in the traditional methods, because this method can make full use of the current test data and the previous data, while the traditional methods can only use current test data. Thus, fewer specimens are required in the two dimensional up and down method and the result is more accurate for the same number of specimens. A contrast example is also given in the paper.

Key words: up-and-down met hod, r elia bility, fatigue test, impact t est