varianceof the total test scores. A formula that is easier to use (not requiring
calculation of item facility) but less accurate than KR20 is KR21, which
is based on information about (a) the number of items on the test, (b) the
meanof the test, and (c) the varianceof the total test scores, all of which
are readily available, but requires an assumption that all items are equal in
item difficulty.
see also Cronbach alpha, internal consistency reliabilitykurtosisn
a measure of the extent to which the peak of a distribution departs from
the shape of the peak of a normal distribution. When the peak of a dis-
tribution is more pointed than a normal distribution, the shape of the
peak is described as leptokurtic, whereas when the peak is flatter, the shape
is called platykurtic.
kurtosis