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In some cases an unbiased efficient estimator exists , which , in addition to having the lowest variance among unbiased estimators , satisfies the Cramér–Rao bound , which is an absolute lower bound on variance for statistics of a variable .
 Cramér–Rao
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Cramér–Rao