They also tend to reduce wage disparities between age groups and sexes, since low-paid workers are often young or female.

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Primark has proved one of the UK High Street's unquestioned success stories in recent years, its mixture of low prices and accessible fashion proving a hit with varying age groups.

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In addition to looking at personal characteristics such as age and relationship status, the researchers divided the countries into high- and middle-to-low income groups according to average household earnings.

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So they end up pooling groups of people by such basic factors as age, occupation and postcode, which means that some low-risk customers are lumped in with risky ones and subsidise their cover.

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