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As the launch date for the RCPCHGrowth API approaches, it is interesting to reflect on how the process of going electronic has affected the calculations...
(a thread)
(a thread)
Age in chart references is decimalised - that is, the age in days is divided by 365.25 to become decimal years (the extra quarter day to take account of the leap year every 4 years)
When plotting a measurement against age on a growth chart, it is crucial to calculate the age correctly, or the measurement will be plotted incorrectly, leading to errors. The scale on the charts is laid out in weeks and months to make it easier if you are plotting on paper...
The gridlines are there to guide professionals to minimise error. But if a computer is plotting the dots, who needs gridlines?
Another effect is on age correction. If babies are born preterm (before 37 weeks in a 40 week pregnancy), clinicians calculate two ages: the age taking account of gestation at birth ('adjusted or corrected' age) and their age using their due date instead of their birth date.
Convention has it that a measurement in a preterm baby is plotted twice - at their uncorrected or chronological age with a dot, and at the corrected age with a cross. They are joined by an 'arrow back'.
This can make charts busy, and harder to plot accurately. Once term, convention has said that age correction (say at 38 weeks) would be so small and impractical to plot on paper that we stop correcting at that point; so that for the 5 weeks 37-42 weeks the ages are all the same.
As are the LMS values used to calculate a centile. But of course a computer can plot these measurements accurately at any age, so as a consequence of this, the RCPCH Growth Chart Project Board have ruled that age correction can happen at all gestations, even when term....
..in addition, in the same way that age correction is harder to calculate and plot the older you get (and has less meaning), convention has it that age correction stops at 1 year if you were born at 32 weeks or above, and for 2 years if you were born below 32 weeks.
But a computer can correct for these small differences and plot them accurately without difficulty at any age. So with this in mind some quite far reaching changes have happened in the world of children's growth:
1. Correction for gestation will be made for all babies, even those born after 37 weeks
2. Age correction will happen across the life course, not just up to 1 or 2 y.
This is possible because RCPCHGrowth API can take the errors away and plot beautiful accurate charts, every time.
2. Age correction will happen across the life course, not just up to 1 or 2 y.
This is possible because RCPCHGrowth API can take the errors away and plot beautiful accurate charts, every time.
