Post+Hoc+Analysis

=Post Hoc (Expected Findings) (GWU EMSE 216-8000)=

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"**Post-hoc analysis**, in the context of [|design] and analysis of experiments, refers to looking at the data—after the experiment has concluded—for patterns that were not specified //[|a priori]//. It is sometimes called by critics //[|data dredging]// to evoke the sense that the more one looks the more likely something will be found. More subtly, each time a pattern in the data is considered, a [|statistical test] is effectively performed. This greatly inflates the total number of statistical tests and necessitates the use of [|multiple testing] procedures to compensate. However, this is difficult to do precisely and in fact most results of post-hoc analyses are reported as they are with unadjusted [|//p//-values]. These //p//-values must be interpreted in light of the fact that they are a small and selected subset of a potentially large group of //p//-values. Results of post-hoc analysis should be explicitly labeled as such in reports and publications to avoid misleading readers.

" In practice, post-hoc analysis is usually concerned with finding patterns in [|subgroups] of the sample." - [|Wkipedia]

While it seems like a good way to get some answers, "when a large number of associations can be looked at in a dataset where only a few real associations exist, a P value of 0.05 is compatible with the large majority of findings still being false positives.w7 These false positive findings are the true products of data dredging, resulting from simply looking at too many possible associations. One solution here is to be much more stringent with “significance” levels, moving to P<0.001 or beyond, rather than P<0.05."

Post hoc analysis is not a preferred EMSE (method) ( Question_Q ?" ToDo - more


 * Sources**
 * EMSE 8000, Spring 2011 Syllabus
 * Post-hoc analysis. (2011, March 26). In Wikipedia, The Free Encyclopedia. Retrieved 14:03, March 27, 2011, from []
 * Title: Data dredging, bias, or confounding - They can all get you into the BMJ and the Friday papers Author(s): Smith, GD Source: BRITISH MEDICAL JOURNAL Volume: 325 Issue: 7378 Pages: 1437-+ Published: DEC 21 2002 Accessed March 27, 2011 from []

Contributors: Sisson