In survey methodology, the design effect (generally denoted as or ) is the ratio between the variances of two estimators to some parameter of interest. Specifically the ratio of an actual variance of an estimator that is based on a sample from some sampling design, to the variance of an alternative estimator that would be calculated (hypothetically) using a sample from a simple random sample (SRS) of the same number of elements. It measures the expected effect of the design structure (such as correlations among clusters of observations, unequal probability of sampling, etc.) on the variance of some estimator of interest. The design effect is a positive real number that can indicate an inflation , or deflation in the variance of an estimator for some parameter, that is due to the stud