Abstract
An attempt has been made to improve upon the Hansen-Hurwitz (1943) estimator based on PPSWR sampling scheme through Rao-Blackwellisation. In order to derive the sampling variance of the improved estimator obtained by Rao-Blackwellisation, it is of interest to derive the probability distribution of the number of distinct units in the sample drawn according to PPSWR sampling scheme, as the improved estimator is based solely on the distinct units in the sample. It has been possible to write down the exact distribution of the number of distinct units in the sample drawn by PPSWR sampling scheme in a closed form. Assuming a super-population model, the model-expected design-variance of the improved estimator is worked out and it is compared with that of the Hansen-Hurwitz estimator under the same super-population model. The percentage gain in efficiency in using the improved estimator over the Hansen-Hurwitz estimator is worked out for certain selected values of the model parameters. AMS (2000) Subject Classification : 62D05.
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