On 2012-06-26 23:02, John wrote:
On Wed, 27 Jun 2012 16:58:29 +1200
Rolf Turner<rolf.tur...@xtra.co.nz> wrote:
On 27/06/12 08:54, arun wrote:
Hi,
The error is due to less than 5 observations in some cells.
NO, NO, NO!!!! It's not the observations that matter, it is
the ***EXPECTED COUNTS***. These must all be at least
5 in order for the null distribution of the test statistic to be
adequately approximated by a chi-squared distribution.
cheers,
Rolf Turner
Pretty sure the point was that in a situation where the expected counts
are too low for a reliable chi-square, that an alternate test such as
the nonparametric Fisher's Exact Test may be the way to go, especially
if there isn't nay more data to get. That way you don't have to worry
about expected counts.
JDougherty
That may well be; nevertheless, the post included the statement
Rolf quotes: "... less than 5 _observations_ in some cells" (my
emphasis). And Rolf's point is quite correct - it's the
_expected_ counts that the approximation cares about.
Peter Ehlers
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