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R: Data Analysis and Visualization by Ágnes Vidovics-Dancs, Kata Váradi, Tamás Vadász, Ágnes Tuza, Balázs Árpád Szucs, Julia Molnár, Péter Medvegyev, Balázs Márkus, István Margitai, Péter Juhász, Dániel Havran, Gergely Gabler, Barbara Dömötör, Gergely Daróczi, Ádám Banai, Milán Badics, Ferenc Illés, Edina Berlinger, Bater Makhabel, Hrishi V. Mittal, Jaynal Abedin, Brett Lantz, Tony Fischetti

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Testing more than two means

Another really common situation requires testing whether three or more means are significantly discrepant. We would find ourselves in this situation if we had three experimental conditions in the blood pressure trial: one groups gets a placebo, one group gets a low dose of the real medication, and one groups gets a high dose of the real medication.

Hmm, for cases like these, why don't we just do a series of t-tests? For example, we can test the directional alternative hypotheses:

  • The low dose of blood pressure medication lowers BP significantly more than the placebo
  • The high dose of blood pressure medication lowers BP significantly more than the low dose

Well, it turns out that doing this first is pretty dangerous business, ...

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