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BMJ小小統計問題(5)

前言：

什麼是P value？這問題是假設考驗非常重要的基本問題！建議必讀！

題目：

下列針對P值的敘述何者正確？

Which one statement is true of the P value?

a) 它指虛無假設為真的機率 (It is the probability that the null hypothesis is true)

b) 它指對立假設為真的機率 (It is the probability that the alternative hypothesis is true)

c) 它指虛無假設錯誤的機率 (It is the probability that the null hypothesis is false)

d) 它指對立假設錯誤的機率 (It is the probability that the alternative hypothesis is false)

e) 它指當虛無假設為真，則比已知結果或更極端結果發生的機率 (It is the probability of the given result or more extreme results if the null hypothesis were true).

Answer：

Statistical testing doesn’t quite do what clinicians would wish for. We are interested to know how near the truth a study result is likely to be. Standard statistics start from a the theoretical probability distribution and give answers to questions such as: “If this study were based on completely random data, how unusual would these actual results be?”

統計檢驗並沒有達到臨床醫生所希望的結果。我們想知道研究結果與事實有多接近。標準統計學從理論概率分佈開始，並回答如下問題:“如果這項研究是基於完全隨機的數據，那麼這些實際結果會有多不尋常(常見)?”

Answer a) is frequently assumed to be the practical interpretation of a P value. It is not strictly correct, but for most people (except under exam conditions) that will not matter much when working to this assumption.

答案a)通常被認為是P值的實際解釋。嚴格來看，它並不正確，但對於大多數人(除了在考試條件下)，按照這一假設進行操作並沒有甚麼問題

答案是選擇 e)，我們假設H0(虛無假設)是對的，然後使用實際樣本資料進行分析，檢視在H0成立的時候，樣本以及更極端樣本發生的概率。正如前面所述，選項a)在考試的時候不能這麼理解，但對於醫務工作者（公共衛生除外），沒這麼嚴格要求。