Some 20 to 30 years ago considerable progress was made in understanding the variance of mortality rates and, for assured lives data, the effect on it of the presence of duplicate policies, e.g. Redington and Michaelson (1940), Seal (1941, 1947, 1948 and 1949), Daw (1945 and 1951), Vajda (1945), Solomon (1948), Beard (1951), Jager (1953) and Continuous Mortality Investigation (C.M.I.) (1957). I have the impression that since that time this understanding has tended to regress. For example it is disappointing to find that the whole course of reading on the analysis of mortality data makes practically no mention of the effect of duplicate policies in increasing the variance of mortality rates. Yet this is a matter which can have a substantial effect on the results of testing a mortality table graduation as is recognized in C.M.I. (1974). It is salutory to find that G. H. Hardy (1882) was aware that the presence of duplicates increased the variance although he did not express it in quite that way.