On the TV and radio forcasts this morning much publicity was given to
the heavy rainfall in Cumbria yesterday. It was stated several times
that the rainfall "yesterday" may be a new daily record for June. They
may have been referring in advance to the 24-hour period ending at
0900z today or they may have been referring to some other period,
perhaps the 24 hours ending at 1800z yesterday. Surely, though, when
considering such a record what matters is the maximum fall during any
24-hour period rather than the 24 hours ending at some arbitrarily
chosen hour. For example, if 100 mm falls on a given day between 0000z
and 1800z, equally distributed throughout the period, this would give
two 0900z-0900z days with 50 mm each which would be trumped by another
day with a fall of 60 mm spread over a single 0900z-0900z day. Clearly,
the 100 mm fall in 18 hours would be the more significant event but it
would be lost in the 0900-0900z reporting convention.

Just one of many ways in which statistics can give misleading
information to the unwary.

--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.
https://peakdistrictweather.org
twitter: @TideswellWeathr