estimator

n. person who estimates, assessor

In statistics, an estimator is a function of the observable sample data that is used to estimate an unknown population parameter; an estimate is the result from the actual application of the function to a particular set of data. Many different estimators are possible for any given parameter. Some criterion is used to choose between the estimators, although it is often the case that a criterion cannot be used to clearly pick one estimator over another. To estimate a parameter of interest (e.g., a population mean, a binomial proportion, a difference between two population means, or a ratio of two population standard deviation), the usual procedure is as follows:Select a random sample from the population of interest.Calculate the point estimate of the parameter.Calculate a measure of its variability, often a confidence interval.Associate with this estimate a measure of variability.
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(n.)
One who estimates or values; a valuer.
  

Noun
1. an expert at calculation (or at operating calculating machines)
(synonym) calculator, reckoner, figurer, computer
(hypernym) expert
(hyponym) adder
(derivation) calculate, estimate, reckon, count on, figure, forecast

estimator