Conflating variables: Down’s syndrome

A very interesting BBC article that also highlights the possible issues with drawing conclusions where variables are conflated.

It covers the increasing prevalence of babies born with Down’s syndrome, both in terms of raw numbers of births and the proportion of Down’s births to total births.

With 717 births in 1989 before the pre-natal test was introduced, the number fell to 594 in 2000, but has since risen to 749 in 2006. The percentage of births of which the baby has Down’s syndrome has also increased by 15% since 2000.

One argument cited for the increase in numbers since 2000 is that society has become more accepting of the condition. An alternative argument is the increasing average age of child-bearing women, something that itself increases the propensity for conceiving a foetus with Down’s syndrome.

Identifying the genuine reason for the trend would require more data, specifically the abortion rates over time of foetuses vs. the risk assessments resulting from the triple test performed.


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