Editing 1478: P-Values
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The chart labels a ''p''-value of exactly 0.050 as "Oh crap. Redo calculations" because the ''p''-value is very close to being considered significant, but isn't. The desperate researcher might be able to redo the calculations in order to nudge the result under 0.050. For example, problems can often have a number of slightly different and equally plausible methods of analysis, so by arbitrarily choosing one it can be easy to tweak the ''p''-value. This could also be achieved if an error is found in the calculations or data set, or by erasing certain unwelcome data points. While correcting errors is usually valid, correcting only the errors that lead to unwelcome results is not. Plausible justifications can also be found for deleting certain data points, though again, only doing this to the unwelcome ones is invalid. All of these effectively introduce sampling bias into the reports. | The chart labels a ''p''-value of exactly 0.050 as "Oh crap. Redo calculations" because the ''p''-value is very close to being considered significant, but isn't. The desperate researcher might be able to redo the calculations in order to nudge the result under 0.050. For example, problems can often have a number of slightly different and equally plausible methods of analysis, so by arbitrarily choosing one it can be easy to tweak the ''p''-value. This could also be achieved if an error is found in the calculations or data set, or by erasing certain unwelcome data points. While correcting errors is usually valid, correcting only the errors that lead to unwelcome results is not. Plausible justifications can also be found for deleting certain data points, though again, only doing this to the unwelcome ones is invalid. All of these effectively introduce sampling bias into the reports. | ||
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Values between 0.051 and 0.06 are labelled as being "on the edge of significance". This illustrates the regular use of "creative language" to qualify significance in reports, as a flat "not significant" result may look 'bad'. The validity of such use is of course a contested topic, with debates centering on whether ''p''-values slightly larger than the significance level should be noted as nearly significant or flatly classed as not-significant. The logic of having such an absolute cutoff point for significance may be questioned. | Values between 0.051 and 0.06 are labelled as being "on the edge of significance". This illustrates the regular use of "creative language" to qualify significance in reports, as a flat "not significant" result may look 'bad'. The validity of such use is of course a contested topic, with debates centering on whether ''p''-values slightly larger than the significance level should be noted as nearly significant or flatly classed as not-significant. The logic of having such an absolute cutoff point for significance may be questioned. |