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Theory of Statistics - George Mason University

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504 7 Statistical Hypotheses and Confidence Sets<br />

a level <strong>of</strong> confidence that corresponds to the level <strong>of</strong> significance <strong>of</strong> the test.<br />

The basic ideas <strong>of</strong> confidence sets were discussed in Section 3.5.2, beginning on<br />

page 292. The related concept <strong>of</strong> credible sets was described in Section 4.6.1,<br />

beginning on page 368. Beginning in Section 7.1 <strong>of</strong> the present chapter, we<br />

discuss confidence sets in somewhat more detail.<br />

The Decisions in Hypothesis Testing<br />

It is in hypothesis testing more than in any other type <strong>of</strong> statistical inference<br />

that the conflict among various fundamental philosophies come into sharpest<br />

focus.<br />

Neyman-Pearson; two<br />

Fisher significance test; one<br />

one, where the other is “all others”<br />

evidence as measured by likelihood<br />

7.1 Statistical Hypotheses<br />

A problem in statistical hypothesis testing is set in the context <strong>of</strong> a given<br />

broad family <strong>of</strong> distributions, P = {Pθ : θ ∈ Θ}. As in other problems in<br />

statistical inference, the objective is to decide whether the given observations<br />

arose from some subset <strong>of</strong> distributions PH ⊆ P.<br />

The statistical hypothesis is a statement <strong>of</strong> the form “the family <strong>of</strong> distributions<br />

is PH”, where PH ⊆ P, or perhaps “θ ∈ ΘH”, where ΘH ⊆ Θ.<br />

The full statement consists <strong>of</strong> two pieces, one part an assumption, “assume<br />

the distribution <strong>of</strong> X is in the class”, and the other part the hypothesis,<br />

“θ ∈ ΘH, where ΘH ⊆ Θ.” Given the assumptions, and the definition <strong>of</strong> ΘH,<br />

we <strong>of</strong>ten denote the hypothesis as H, and write it as<br />

Two Hypotheses<br />

H : θ ∈ ΘH. (7.1)<br />

While, in general, to reject the hypothesis H would mean to decide that<br />

θ /∈ ΘH, it is generally more convenient to formulate the testing problem as<br />

one <strong>of</strong> deciding between two statements:<br />

and<br />

H0 : θ ∈ Θ0<br />

(7.2)<br />

H1 : θ ∈ Θ1, (7.3)<br />

where Θ0 ∩Θ1 = ∅. These two hypotheses could also be expressed as “the family<br />

<strong>of</strong> distributions is P0” and “the family <strong>of</strong> distributions is P1”, respectively,<br />

with the obvious meanings <strong>of</strong> P0 and P1.<br />

We do not treat H0 and H1 symmetrically; H0 is the hypothesis (or “null<br />

hypothesis”) to be tested and H1 is the alternative. This distinction is important<br />

in developing a methodology <strong>of</strong> testing.<br />

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

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