In: Statistics and Probability
Let 𝑋1, 𝑋2,…, 𝑋𝑛 be a random sample of a gamma distribution with parameters 𝛼 (known) and 𝛽 (unknown), prove that 𝑇 (𝑿) = 𝑋̅ is a sufficient estimator for 𝛽.
Let  
be a random sample from the pdf or pmf 
 . Then the statistics 
 is sufficient for 
 , iff we can factorize the joint  PDF and PMF of
 as 
Where 
 depends on 
 but not on 
 and 
 depends on 
 and on 
 only through 
In our problem 
  
with pdf :
Join density function is given by:

Now let,
Cleraly 
  depends on 
 but not on 
But 
 depends depends on 
 and on 
 only through 
Hence factorization theorem implies   
is sufficient Statistics for estimator