at birth or in the population as a whole, might be quoted in any of four ways: the ratio of males to females, the ratio of females to males, the proportion of males, or the proportion of females. If there are 108,000 males and 100,000 females, the ratio would be quoted as 1.080. Sex ratio in scientific literature is often expressed as the proportion of males. In contrast, sex ratio quoted in this article is the ratio of males to females, unless specified otherwise. In a study around 2002, the natural sex ratio at birth was estimated to be close to 1.06 males/female. [ 5 ] In most populations, adult males tend to have higher death rates than adult females of the same age (even after allowing for causes specific to females such as death in childbirth), both due to natural causes such as heart attacks and strokes, which account for by far the majority of deaths and also to violent causes, such as homicide and warfare (for example, in the USA as of 2006, an adult non-elderly male is 3 to 6 times more likely to become a victim of a homicide and 2.5 to 3.5 times more likely to die in an accident than a female of the same age), [ 6 ] resulting in higher life expectancy of females. Consequently, the sex ratio tends to reduce as age increases, and among the elderly there is usually an excess of females. For example, the male to female ratio