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GATE 2020 ST – Question 44

Estimation · Sufficiency and Completeness · 2 marks · Multiple choice

X₁,…,Xn,n≥2, have density θ⁻¹exp[−(x−θ)/θ] for x>θ, θ>0. Which statement is true?

  1. The sample minimum is minimal sufficient.
  2. The sample sum is minimal sufficient.
  3. Every minimal sufficient statistic is complete.
  4. (sample minimum,sample mean) is minimal sufficient.

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Correct answer: (D) (sample minimum,sample mean) is minimal sufficient.

Explanation

Likelihood is θ⁻ⁿexp[n−Σxi/θ] times the support indicator θ<min xi. Its parameter-dependent factors require both the sum and minimum. The likelihood ratio is constant inθ exactly when both agree, establishing minimal sufficiency. Mean is equivalent to sum, so D.

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