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ICAR JRF Computer Application 29 Jun 2024Shift 1
MCQ (Single Correct) +4 −1
‘Two samples of size n ate selected, one according to SRSWR and the other according to SRSWOR. Under SRSWR, V; stands for variance of sample mean based on all units while V2 stands for the variance of sample mean based on distinct units. V3 stands for the variance of sample mean based on SRSWOR. Which one of the following holds ?
  • Comparison of Variances in SRSWR and SRSWOR:
  • Let $V_1$ be the variance of the sample mean based on all $n$ units under SRSWR:
$$V_1 = \frac{N-1}{N} \frac{S^2}{n} = \frac{\sigma^2}{n}$$
  • Let $V_2$ be the variance of the sample mean based on distinct units $d$ under SRSWR (using the Rao-Blackwellized estimator $\bar{y}_d$, where $E[d] \lt n$):
$$V_2 = V(\bar{y}_d) \lt V_1$$
  • Let $V_3$ be the variance of the sample mean under SRSWOR of the same fixed size $n$:
$$V_3 = \frac{N - n}{N} \frac{S^2}{n} = \left(1 - \frac{n}{N}\right) \frac{S^2}{n}$$
  • Theoretical Ordering: Since repeated sampling adds redundant units in SRSWR, discarding duplicate units strictly improves efficiency ($V_1 \ge V_2$). Furthermore, a direct SRSWOR sample of fixed size $n$ always achieves at least as many distinct units as SRSWR, giving:
$$V_1 \ge V_2 \ge V_3$$
  • Conclusion: The relationship that holds is $V_1 \ge V_2 \ge V_3$ (Option 1).

Correct option: (1) V42V22V3

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