Locating Variance: Post-Hoc Tests. Developing Study Skills and Research Methods (HL20107). Dr James Betts. It is easy (i.e. data in P value out) It provides the ‘Illusion of Scientific Objectivity’ Everybody else does it. Why do we use Hypothesis Testing?.
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Developing Study Skills and Research Methods (HL20107)
Dr James Betts
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We accept ‘significance’ and reject the null hypothesis at P0.05 (i.e. a 5% chance that we are wrong)
Performing multiple tests therefore means that our overall chance of committing a type I error is >5%.Why not multiple t-tests?
Recovery Supp. 1
Recovery Supp. 2
See also Perneger (1998) BMJ 316: 1236
Multiple t-tests with a Bonferroni correction are more appropriate for aspherical data
Stepwise correction of standard Bonferroni procedures maintain power with factorial designs
Best option is to keep your study simple:
Pre-planned contrast at a specific time point
Summary statistics (e.g. rate of change, area under curve)
Just make an informed based on the data available.Summary Post-Hoc Tests