rcpchgrowth

Age bands

Since the introduction of CDC, which uses a different centile format collection, the centile band advice is nolonger accurate. UK-WHO use 2/3 SDS intervals between centiles, so that the collection becomes 0.4th (-2.67SDS), 2nd (-2SDS), 9th (-1.33), 25th (-0.67), 50th (0 SDS), 75th, 91st, 98th, 99.6th - these are termed 'cole-nine-centiles' as a collection name for shorthand CDC uses a mixture of centiles in their charts - standard is termed 'five-percent-centiles', comprising 5th, 10th, 25th, 50th, 75th, 90th, 95th. For depicting more extremes, 3rd centile is added and is termed 'three-percent-centiles'. The extended BMI release of 2022 included here recognised the significant impact of obesity on population health and sought to reflect this in the charting. It recognised the difficulties of using SDS at higher values discussed elsewhere and introduced a further parameter (sigma) in the LMS dataset, which defines dispersion or spread of all BMI measurements above the 95th centile (p95). sigma = sqrt(2) * S * exp(L * (log(BMI/M) - log(P95/M))) This has allowed the introduction of a new centile collection, termed 'eight-five-percent-centiles' which include all those in the five-percent-centiles with the additional 85th, 90th, 95th, 99.9th, 99.99th.

While this is all implemented for CDC in RCPCHGrowth, the centile_band is text for lay users to know how far the measurement is from the nearest centile. The Measurement class though cannot know what sort of chart it is being plotted on so the solution here is to produce advice based on the standard chart for reference and measurement_method.