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Theory of Statistics - George Mason University

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316 3 Basic Statistical <strong>Theory</strong><br />

(1967) expanded on these relations. In a two-person game, one player, “nature”,<br />

chooses action “θ” and the other player, “the statistician”, chooses<br />

action “a” and the elements <strong>of</strong> the pay<strong>of</strong>f matrix are the values <strong>of</strong> the loss<br />

function evaluated at θ and a.<br />

Complete Class Theorems<br />

Wald, starting in Wald (1939) and especially in Wald (1947a), gave the first<br />

characterizations <strong>of</strong> a class <strong>of</strong> decision rules that are complete or are essentially<br />

complete. These theorems are collected in Wald (1950). See also<br />

Kiefer (1953), who proved some additional properties <strong>of</strong> complete classes, and<br />

Le Cam (1955), who relaxed some <strong>of</strong> the assumptions in the theorems.<br />

Estimating Functions and Generalized Estimating Equations<br />

The idea <strong>of</strong> an estimating function is quite old; a simple instance is in<br />

the method <strong>of</strong> moments. A systematic study <strong>of</strong> estimating functions and<br />

their efficiency was begun independently by Godambe (1960) and Durbin<br />

(1960). Small and Wang (2003) provide a summary <strong>of</strong> estimating functions<br />

and their applications. Estimating functions also play a prominent role in<br />

quasi-likelihood methods, see Heyde (1997). We will discuss this further in<br />

Chapter 6.<br />

Unbiasedness<br />

The concept <strong>of</strong> unbiasedness in point estimation goes back to Gauss in the<br />

early nineteenth century, who wrote <strong>of</strong> fitted points with no “systematic error”.<br />

Although nowadays unbiasedness is most <strong>of</strong>ten encountered in the context<br />

<strong>of</strong> point estimation, the term “unbiased” was actually first used by statisticians<br />

to refer to tests (Neyman and Pearson, 1936, cited in Lehmann (1951)),<br />

then used to refer to confidence sets (Neyman, 1937, cited in Lehmann (1951)),<br />

and later introduced to refer to point estimators (David and Neyman, 1938,<br />

cited in Lehmann (1951)). See Halmos (1946) and Lehmann (1951) for general<br />

discussions, and see page 292 for unbiased tests and page 296 for unbiased<br />

confidence sets. The idea <strong>of</strong> unbiasedness <strong>of</strong> an estimating function was introduced<br />

by Kendall (1951).<br />

In a decision-theoretic framework, L-unbiasedness provides an underlying<br />

unifying concept.<br />

Equivariant and Invariant Statistical Procedures<br />

Equivariant and invariant statistical models have a heuristic appeal in applications.<br />

The basic ideas <strong>of</strong> invariance and the implications for statistical<br />

inference are covered in some detail in the lectures <strong>of</strong> Eaton (1989).<br />

<strong>Theory</strong> <strong>of</strong> <strong>Statistics</strong> c○2000–2013 James E. Gentle

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