Mark Wadsworth

This is a spare 'blog in case my main 'blog at isn't working

Smoking horror statistics – missing figures round

From the BBC:

Women who smoke while pregnant should be aware that they are increasing the chance their baby will be born malformed, say experts. The risk for having a baby with missing or deformed limbs or a cleft lip is over 25% higher for smokers, data show.

Along with higher risks of miscarriage and low birth weight, it is another good reason to encourage women to quit, say University College London doctors. In England and Wales 17% of women smoke during pregnancy. And among under 20s the figure is 45%.

Although most will go on to have a healthy baby, smoking can cause considerable damage to the unborn child. Researchers now estimate that each year in England and Wales several hundred babies are born with a physical defect directly caused by their mother’s smoking. Every year in England and Wales around 3,700 babies in total are born with such a condition.

OK, 3,700 babies are born with defects out of 750,000 babies a year. We can minus off a third of those caused by Pakistanis marrying their first cousins, which gets it down to a third of a per cent with defects, call it 2,500 a year.

Question 1: If 17% of women smoke; the overall average risk of a baby born to normal couple having a defect is 0.33%; and the risk of your baby having a defect is 25% higher if you smoke (they cherry picked diseases where the risk is measurably higher, and didn’t mention all the defects where the risk is the same whether you smoke or not, but hey), then what are the chances of having a baby with a defect if you:
a) Don’t smoke during pregnancy.
b) Smoke during pregnancy.

Click and highlight to reveal answers: a) 0.32%, b) 0.4% (you can guess this answer, one is 0.33% minus a tiny bit and the other is 0.33% plus five tiny bits).

Question 2: How many babies born to mothers who smoke will have birth defects?

Click and highlight to reveal answer: 750,000 babies x 17% smokers x 0.4% with defects = 510 babies.

Question 3: If those mothers hadn’t smoked, how many of their babies would have birth defects anyway?

Click and highlight to reveal answer: 750,000 babies x 17% x 0.32% = 408.

Question 4: Deduct your answer from 3 from your answer from 2 to calculate the additional number of babies born with defects as a result of the mother smoking?

Click and highlight to reveal answer: 510 – 408 = 102. It’s not “several hundred”, is it? There’s a wide margin of error here, but I’d politely refer to that as “one hundred”, i.e. a tenth as many as babies born with defects due to inbreeding.


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