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The mathematics of parenthood…..

In July I became a father for the first time. This is an immensely wonderful, emotional and at times terrifying experience. After the birth you are very much left to learn by doing, and we have been enjoying parenthood ever since.

One of the things they give you when you become parents is “The red book” (http://www.rcpch.ac.uk/PCHR). In this book the health visitors/midwives and Dr’s keep everything they write about your child, and there are bits for you to fill in. The bits that captured my interest the most were the charts at the back pertaining to baby’s weight and height (length). My daughter was born at the 50th percentile (the median) weight for a little girl, but very quickly jumped up to the section of the chart between the 67th and 91st percentile, and is now moving along at the 91st.


My partner and I were looking through the book last week and noticed that she (our daughter) had never been measured for length, I looked at the chart for her age and the 91st percentile and said, “she should be 68 cm long.” We then measured her, and she was ever so slightly over that (68.2cm).


We were quite amazed by how accurate the chart had been. I wonder how they work it out? I assume there is a huge bank of data records and that these were probably normalised and the charts derived from the normal distribution, but I would love to see the full report on the maths. The databank must be massive! All babies born since ”records began” !!!!

We then got a bit carried away and extrapolated some data, hypothesising the following:

• When she is an adult she will be 5’ 7” tall and weigh 11 stone 5lb


• If she were a boy she would be 70cm in length and weigh 18lb
• As a male adult she would be 6’ 1” tall and weigh 13 stone 4lb

Obviously hypothesis 2 and 3 are untestable, and as such a thought experiment. However, check back here in 20 years time to see how accurate hypothesis 1 is!

It made me wonder if this was relevant to my students. The school have had teen pregnancies, and the area we are in is a teen pregnancy hotspot. There are many pupils, generally female, who study health and social care and child development at our school, so there is cross curricular opportunities. The majority of the pupils will become parents themselves at some stage, as the majority of humans do. Given these facts I decided that this would be very relevant to them, and I am planning to investigate ways of incorporating this next time stats comes around! (Plus, it will give me an excuse to show off some baby photos!)









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