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Which of the following is NOT true for stratified random sampling ?

A larger sample would be required from a stratum if :

  • A.stratum size is large
  • B.stratum variability is large
  • C.sampling cost per unit is large in the stratum
  • D.sampling cost per unit is small in the stratum

Answer: C

The statement that is NOT true is that a larger sample is needed when the sampling cost per unit is large in the stratum.

Under optimum allocation the sample size in stratum h is

\[ n_{h} \propto \frac{N_{h} S_{h}}{\sqrt{c_{h}}} \]

It grows with the stratum size \(N_{h}\) and the stratum variability \(S_{h}\), and falls as the cost per unit \(c_{h}\) rises. So a costly stratum gets a smaller sample, not a larger one.

Options A, B and D (large size, large variability, low cost) all correctly call for a larger sample.

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