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Twisting properties
・ Twisting the Jug
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Twisting properties : ウィキペディア英語版
Twisting properties

Starting with a sample \ observed from a random variable ''X'' having a given distribution law with a non-set parameter, a parametric inference problem consists of computing suitable values – call them estimates – of this parameter precisely on the basis of the sample. An estimate is suitable if replacing it with the unknown parameter does not cause major damage in next computations. In algorithmic inference, suitability of an estimate reads in terms of compatibility with the observed sample.
In turn, parameter compatibility is a probability measure that we derive from the probability distribution of the random variable to which the parameter refers. In this way we identify a random parameter Θ compatible with an observed sample.
Given a sampling mechanism M_X=(g_\theta,Z), the rationale of this operation lies in using the ''Z'' seed distribution law to determine both the ''X'' distribution law for the given θ, and the Θ distribution law given an ''X'' sample. Hence, we may derive the latter distribution directly from the former if we are able to relate domains of the sample space to subsets of Θ support. In more abstract terms, we speak about twisting properties of samples with properties of parameters and identify the former with statistics that are suitable for this exchange, so denoting a well behavior w.r.t. the unknown parameters. The operational goal is to write the analytic expression of the cumulative distribution function F_\Theta(\theta), in light of the observed value ''s'' of a statistic ''S'', as a function of the ''S'' distribution law when the ''X'' parameter is exactly θ.
==Method==
Given a sampling mechanism M_X=(g_\theta,Z) for the random variable ''X'', we model \boldsymbol X=\ to be equal to \. Focusing on a relevant statistic S=h_1(X_1,\ldots,X_m) for the parameterθ, the master equation reads
:s= h(g_\theta(z_1),\ldots, g_\theta(z_m))= \rho(\theta;z_1,\ldots,z_m).
When ''s'' is a well-behaved statistic w.r.t the parameter, we are sure that a monotone relation exists for each \boldsymbol z=\ between ''s'' and θ. We are also assured that Θ, as a function of \boldsymbol Z for given ''s'', is a random variable since the master equation provides solutions that are feasible and independent of other (hidden) parameters.〔By default, capital letters (such as ''U'', ''X'') will denote random variables and small letters (''u'', ''x'') their corresponding realizations.〕
The direction of the monotony determines for any \boldsymbol z a relation between events of the type s\geq s'\leftrightarrow \theta\geq \theta' or ''vice versa'' s\geq s'\leftrightarrow \theta\leq \theta', where s' is computed by the master equation with \theta'. In the case that ''s'' assumes discrete values the first relation changes into s\geq s'\rightarrow \theta\geq \theta'\rightarrow s\geq s'+\ell where \ell>0 is the size of the ''s'' discretization grain, idem with the opposite monotony trend. Resuming these relations on all seeds, for ''s'' continuous we have either
:F_(\theta)= F_(s)
or
:F_(\theta)= 1-F_(s)
For ''s'' discrete we have an interval where F_(\theta) lies, because of \ell>0.
The whole logical contrivance is called a twisting argument. A procedure implementing it is as follows.

抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)
ウィキペディアで「Twisting properties」の詳細全文を読む



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