As an earth scientist and road surface specialist I am outisdeof my
comfort zone with accident statistics
I have data for values for KSIs and slights for the months September
to December for 2008 when an
intervention was in place and for the same months for 2005-2007 when it was not
I believe since I cannot show the data is normally distributed, the
wilcoxon rank sum test might be
the best measure of whether 2008 is significantly lower than the other
years (as a group)
I do not have control data to hand nor traffic flows so will have to
state an assumption
Is this test (aka MANN -WHITNEY 'U' ?) a good choice?
Dr B
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