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INTELLIGENCE AND AGEING
The same thing seems to happen with mental abilities too. For example, intelligence is often inaccurately cited as one of the areas which declines with age. For many years, people 'knew' that various abilities, including intelligence and physical strength, reached their peak in the early twenties, and then declined steadily from then on thoughout a person's life. This knowledge was based on a series of studies, resported by Miles in 1931, which involved measuring various human characteristics in people of different ages. When they plotted the results of these measurements on a graph, Miles found a steady decline: the older the person was, the less strong, or intelligent (as measured by IQtests) or able they were.
Other reseachers found similar results, so for a great many years there was a strong belief in an inevitable decline with age. Indeed this belief is still held by a great many people, including some doctors and social workers, but when we look more carefully at the evidence, what we find is actually quite a different picture.
Cross-sectional methods
The problem was that all of these studies were done using cross-sectional methods. That is, the reseacher tested several different groups of people, or different ages. But someone who was 60 in 1930 had experienced quite a different upbringing and lifestyle from someone who was 20 at that time. Their schooling was quite different, their life experiences were quite different, and their standards of living were different too. The same thing applied to cross-sectional studies that were conducted later on in the education and health care which had taken place.
It wasn't surprising, for example, that older people did badly on intelligence tests in the 1960s, when they had experienced an education which consisted, in the main, of leaning large chunks of infomation off by heart. Younger people, by contrast, had experienced a form of education which stressd reasoning and mental skills, and so they naturally performed much better on IQ tests.
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