Saturday, July 12, 2008

Grammes and pounds

Although metric weights and measures have been used in science for donkey's years, they continue to pose problems for the writing of English. Habits may be slowly changing in the face of official intransigence, but English families do expect to be told the weight of a baby in pounds and ounces and to measure the height of their children in feet and inches.

It's a particular problem when you are dealing with obesity because the concept of body mass index is based on the weight, in kilogrammes, divided by the height, in metres squared. That's very hard to calculate when your original information is based on imperial measures.

This is a roundabout way of confessing I was caught out late one night last week. I don't like admitting this because we pride ourselves on our numeracy, our ability to make sense of percentages, probabilities, weights and measures etc. I will tell how it happened and to make sure it does not happen again have placed a metric to imperial converter on the left hand column of this blog.

Quite late I realised that a good story on the survival of frozen embryos had not been written. The press release informed me - or so I thought - that these babies weighed on average about 200g. I reckon to be able to do this calculation in my head. One kg is 2.2 lbs. 200g is one fifth of this - and out the other end came seven pounds. Why? Well like every good primary school child I was using estimation. The report told us that these babies were quite healthy - which to my mind means between 2lb and 12lb. So our initial reports states that the babies weighed about 200g - or seven pounds.

In the cold light of day somebody pointed out the mistake and we set out to correct it. For 200g is more like six ounces - but that seemed incredible. Far too small for a new-born baby to survive.

So back to the original press release and this is what is said: birth weight was also higher – about 200 grams – in the FER group.

What it means to say was: birth weight was also higher – by about 200 grams – in the FER group.

So I can lay some of the blame at the European Society of Human Reproduction and Embryology, which put this out. I'll also double-check the conversions on the calculator. But the journalistic lesson is, as always, if you don't trust something, don't print it.

And here's a link to a US government site which allows you to compute BMI from imperial measurements (feet, inches, stones and pounds)

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