**Design effect DEFF**

A convenient way to evaluate a sampling design is to compare the design variance
of an estimator to the design variance from a references sampling scheme of the
same (expected) sample size. Usually, simple random sampling without replacement
is chosen as reference. For example, for an estimator t_hat of the total T, the
ratio of the two design variances is called the design effect and abbreviated to
DEFF. In practice, an estimate of the design effect is calculated using the
corresponding variance estimators for the sample data set. An estimator of the
design effect is thus
deff_{p(s)}(t_hat) = v_hat_{p(s)}(t_hat)/v_hat_{srs}(t_hat),
where p(s) refers to the actual sampling design.
See page 15 in Lehtonen, R & Pahkinen, E. (2004)