Dr Fisher's Casebook

Abstract

SignificanceVolume 8, Issue 3 p. 112-112 FeaturesFree Access Dr Fisher's casebook Live long and prosper First published: 25 August 2011 https://doi.org/10.1111/j.1740-9713.2011.00504.xAboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat Of all the statistics with which our profession routinely mystifies the public at large, the most consistently misunderstood must be expectation of life. For example, in an otherwise excellent article in The Guardian (April 11th, 2011), the journalist Madeleine Bunting wrote: “Middle age is a modern phenomenon – a hundred years ago, life expectancy was 47.” The English Life Table no. 8 tells us that life expectancy at birth in England was actually 52 years for men and 55 years for women one hundred years ago, but this does not mean that people did not live beyond these ages. This is the average number of years people would live if the mortality rates at this time applied throughout their lives. We can calculate life expectancy at any age, not just at birth, and estimate the remaining average life spans of people living to that age. In 1911, the life expectancies at age 11 were 52 and 55, the same as at birth. In other words, people aged 11 still had 52 or 55 more years in front of them; they could expect to be 63 or 66 when they died. If someone lived to 11, the same average number of years remained to them as when they were born. This is because a lot of people died in infancy. Those who survived this dangerous time would have, 11 years later, as much time as they had had at the beginning. So what happens to those who made it to 40, which we might think of as the start of middle age? In 1911, their life expectancies were 28 and 30 years, giving 40-year-old men an average age at death of 68 and women 70 if death rates remained constant. Half of them might live beyond middle age and become elderly. (Yes, I know I am approximating the median by the mean and that this can be a dubious practice.) The interpretation of life expectancy at birth as the age at which most people die is widespread but wrong. Here are two of my favourite examples. The respected psychologist Dorothy Rowe wrote, again in The Guardian, (July 14th, 2011): “Mothers have always provoked rage and resentment in their adult daughters… In past centuries, daughters could bury their rage and resentment under a concern for duty while they cared for their mothers who, turning 40, rapidly aged, grew frail and died. Now mothers turning 40 are strong and healthy, and only half way through their lives.” What nonsense! Even in English Life Table No. 1, 1841, the life expectancy of women aged 40 was 32 years, hardly a rapid death. The Association of the British Pharmaceutical Industry produced an advertisement which began: “They say life begins at 40. Not so long ago, that's about when it ended.” The advertisement claimed that, had we lived in the nineteenth century, we would have attended many funerals of people who died aged about 40, but in the late twentieth century this did not happen. The conclusion was that this increase in life expectancy since then was because of advances in pharmaceuticals1. More nonsense, of course. We might have attended many funerals of children, as a wander through any old cemetery will show, but adults mostly kept going until their sixties; even in 1841 life expectancies at age 40 were 27 and 28. Dictionary definitions of “expectation” include “act or state of expecting”, “prospect of future good”, and “degree of probability”. There is nothing about its statistical definition as “extreme value in repeat sampling”2. We should not be surprised that expectation of life is misinterpreted. A better name for it might be “average further lifespan”. But until I can persuade the world to adopt this, I shall just have to keep writing to the newspapers. References 1St George, D. (1986) Life expectancy, truth, and the ABPI. The Lancet, 2, 346. CrossrefCASPubMedWeb of Science®Google Scholar 2Kendall, M.G. and Buckland, W.R. (1971) A Dictionary of Statistical Terms, 3rd edn. London: Longman. Google Scholar Volume8, Issue3September 2011Pages 112-112 ReferencesRelatedInformation