In three papers this last week it was interesting to see words such as probability or risk used to describe what I would probably have called, simply, percentages. I might have added terms such as growth, change, share, and concentration, distribution or simply more or less, higher or lower to aid description, analysis or explanation.
This probably reflects my training in economics ‘analytical & descriptive’ in the days before the subject became dominated by mathematical models, followed later by work in data collection via censuses & (mostly social) surveys; this latter day shift towards thinking in terms of probabilities may reflect a more widespread acceptance of the idea that we live in a probabilistic world, or just today’s emphasis on model-building & parameter estimation.
It would be interesting to trace the history of when percentage breakdowns (as in the old joke Population broken down by age & sex) became the norm in the presentation of statistical tables. The early authors of papers in the Journal of the Royal Statistical Society use simple proportions with varying denominators, comparing 5 out of 9 with 7 out of 12, for example. Presumably Victorians were better at knowing which was higher.
The British Hedgehog Survey illustrates population decline with an index (setting the base year to 100), which is interpreted as ‘a measure of the probability of detecting a hedgehog in a particular year relative to the probability in the first year of the survey.’ This set me pondering whether there might be anything to be gained by thinking of, for example, the Consumer Price Index, as a (weighted) probability that any product you put in your trolley at the next visit to the supermarket will have increased in price since last month, rather than as a measure of the ‘thing’ we call inflation.
An engagingly written report Hilary: the most poisoned baby name in US history looks at the risk that a name might suddenly fall out of favour with new parents making that all-important decision about what to call their baby. The author talks of ‘a measurement called the relative risk, where “risk” refers to the proportion of babies given a certain name’ and, even more engagingly, explains how to calculate percentage rates of growth and decline.
The third example came from a magazine article about knife crime in London, which quoted a study of the risk that youngsters living in south London might suffer from various kinds of deprivation such as living in a lone parent family without a father, or poor educational attainment. Here the concept of area-based risk comes closer to implying a cause & effect relationship – the area causes the deprivation.
It is not so long ago that the same sort of statements could have been made about Notting Hill. I wonder if the millionaires & Cabinet Ministers who live there now have any such fears for the future of their own children?
Links
PDF]The state of Britain’s hedgehogs 2011
Hilary: the most poisoned baby name in US history
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