Sifting the evidence

doi:10.1136/bmj.322.7295.1184/a

BMJ 2001;322:1184 ( 12 May )

Letters

Sifting the evidence

Likelihood ratios are alternatives to P values

Statistics must not be confused with science

Perfect understanding seldom happens

Likelihood ratios are alternatives to P values

The first 150 words of the full text of this article appear below.

EDITOR $---$ In their critique of P values Sterne and Davey Smith omit two crucial reasons why P values do not adequately reflectevidence.¹

Firstly, their statement (borrowed from Fisher) that "P values measure the strength of the evidence against the null hypothesis"does not stand up to scrutiny. A small P value means that whatwe observe is possible but not very likely under the null hypothesis.But then life is made up of unlikely events. P values cannot deliverevidence against a hypothesis, no matter how low the cut-off pointfor saying that a result is significant. Short of P=0, there isno such thing as evidence against ahypothesis.

Secondly, if evidence is what the data say then P values fail to qualify. P values are based on factors other than the observeddata, notably on results "more extreme than these." The P valueis literally the . . . [Full text of this article]

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Sifting the evidence $---$ what's wrong with significance tests? • Another comment on the role of statistical methods: Jonathan A C Sterne, George Davey Smith, and D R Cox
BMJ 2001 322: 226-231. [Extract] [Full Text] [PDF]