Mortality at the highest ages

The pattern of mortality at the highest ages has been considered by many authors, including Redington (1969), Humphrey (1970) and Benjamin (1964, 1982). The questions raised have included the following: (a) Is there a definite upper limit to the span of human life, so that q x reaches unity at a finite age? Or does q x tend gradually to unity as age tends to infinity, as happens under the Gompertz and Makeham laws? Or does q x tend to a constant less than unity, as under the Perks formula or the formula which was used to graduate the English Life Tables No. 11 and 12? (b) Has the fall in mortality rates at lower ages been accompanied by a similar fall at the very highest ages? Has the upper tail of the curve of death ( μ x l x ) shifted? (c) Does the lower mortality of females compared with males extend to the very highest ages, or do the rates eventually tend to converge?