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Answers for “为什么似然函数不是概率分布?”

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Understand why

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The likelihood function is not a probability distribution because its integral over the parameter space does not equal 1. It measures how well each parameter value explains the fixed data, rather than assigning probabilities to the parameter values themselves.

Conditions: The data are fixed.; The parameter pp is varied over its space [0,1][0,1].

Meet the concept

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The likelihood function is a function of the unknown parameter θ\theta after the observed data x1,…,xnx_1, \dots, x_n are fixed. It assigns to each candidate parameter value a measure of how likely the observed data are under that parameter.

Conditions: The data x1,…,xnx_1, \dots, x_n are treated as fixed observed constants.; The argument being varied is the parameter θ\theta.

Understand why

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The bars represent the probabilities of all possible outcomes (head counts) for a fixed model. Because they exhaust the entire sample space, their sum must equal 1, which is the defining normalization property of a probability distribution.

Conditions: The coin model is fixed at p=0.5p=0.5.; The number of flips is 10.; kk indexes all possible head counts from 0 to 10.