Letter: And there's a chance of rain on Thursdays

Sir: Norman Pattenden (Letters, 24 July) attempts to explain George Nicholson's findings (Letters, 22 July) that Thursday is the wettest day of the week. No explanation is needed. The variation in the figures for the seven days is purely random, as any statistician can assure you.

The total rainfall for all seven days is 938.9ins, giving an average of 134.13. This average is the 'expected' figure for each day if rainfall is distributed equally over the seven. A chi-square test may be used to compare the seven observed figures with the expected one. The resultant chi-square value of 1.28 for 6 degrees of freedom is far too small to demonstrate any significant difference from expectation. In fact, chance would produce this amount of difference at least 95 times out of 100.

Yours faithfully,

MacDONALD P. JACKSON

Oxford

23 July