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Suppose \(\{X_{1}, X_{2}, \ldots, X_{n}\}\) is a random sample of size \(n\) from the \(U(0, \theta)\) distribution. Then :

  • A.Sample mean \(\bar{X}_{n}\) is consistent for \(\theta\)
  • B.Sample median is cosistent for \(\theta\)
  • C.\(2\bar{X}_{n}\) is consistent for \(\theta\)
  • D.\(X_{(1)}\) is consistent for \(\theta\)

Answer: C

The consistent estimator is \(2\bar{X}_{n}\).

For \(U(0, \theta)\), \(E(X) = \theta/2\). By the law of large numbers \(\bar{X}_{n} \to \theta/2\) in probability, so \(2\bar{X}_{n} \to \theta\): it is consistent (and unbiased, with variance \(\theta^{2}/(3n) \to 0\)).

The others converge to the wrong value: \(\bar{X}_{n}\) and the sample median both tend to \(\theta/2\), and the minimum \(X_{(1)}\) tends to 0. (The maximum \(X_{(n)}\), not offered, would also be consistent for \(\theta\).)

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