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Otherwise, the power associated with equal weights remains greater than that associated with minimum variance weights in any situation.
In these situations, the minimum variance weights correction has good properties and allows for achieving the nominal power.
We used the method of minimum variance weights to allow for varying numbers of eligible women between practices.
Minimum variance weights were used instead of the frequently used cluster size weights because of their advantages in case of unequal cluster sizes [ 29].
If such imbalance in cluster size can be anticipated at the design stage, minimum variance weights correction should be used to inflate the required sample size.
Cluster size inequality may induce a loss of power and must be taken into account at the planning stage by using the minimum variance weights correction.
Similar(43)
For example, let us consider the case of 20 clusters per intervention arm: if the ICC is a priori postulated at 0.005, but in reality equals 0.015, the power associated with constant cluster size decreases from 0.80 to 0.75 only, whereas the power associated with Pareto repartition decreases from 0.80 to 0.68 (with the minimum variance weighting system).
Analyses were weighted for varying cluster sizes using minimum variances weights.
We also construct minimum variance unbiased designs and weights which minimize the loss functions subject to a side condition of unbiasedness.
There is a source of bias in the sample eigenvectors of financial covariance matrices, when unchecked, distorts weights of minimum variance portfolios and leads to risk forecasts that are severely biased downward.
19These assumptions are described and assessed in more detail in Stapleton et al. (2013, Appendix D). 20The minimum variance estimate is a weighted mean of the estimates for the two phases where the weights have been chosen to minimize the variance of the estimate.
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