HadCET CUSUM analysis
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CUSUM analysis - a statistical technique borrowed from the quality control discipline - is deceptively simple to calculate by spreadsheet or even by hand yet a powerful tool for screening out 'noise' and spotting trend changes
- calculate the deviations from mean average
- first value = 0
- second value = first value + first deviation
- third value = second value + second deviation
- and so on
- final value = 0 by definition of average must be so
The thing to look for is abrupt kinks in the graph, which shout 'something changed here'. The chart below - original work by FLUKE - appears to show four distinct trend periods: 1772 to 1892, 1892 to 1932, 1932 to 1988 and 1988 to present
