Bioequivalence and Bioavailability Forum

Group “effect” [Design Issues]

posted by Helmut  – Vienna, Austria, 2019-07-20 16:02 (2012 d 00:14 ago) – Posting: # 20413
Views: 7,791

Hi GM,

❝ […] fixed effects used in general crossover studies and possible reasons for significant results of these fixed effects, I didn't found any relevant reasons for the significant group effect.

The p-value itself tells you nothing. If you set your limit to 0.05, that means that you consider a p-value <0.05 denoting an effect which occurred not by pure chance. The reason for an effect is beyond the reach of statistics.
Think about the subject-term. It is always highly significant.* Recode the common effects to something neutral (say, response → Y, sequence → a, subject → b, period → c, treatment → d ) and provide the data to a statistician without telling the background to evaluate the linear model $$\ln(Y) \sim a+b+c+d$$ or – if you insist on the stupid over-specified one given in the guidelines – $$\ln(Y) \sim a+b(a)+c+d$$ Hey, \(p(b)\) or \(p(b(a)) = 0.00000314\). Now ask for a “reason”.
Answer:

Science is wonderfully equipped to answer the question “How?”
but it gets terribly confused when you ask the question “Why?”   Erwin Chargaff

Ask a physicist what gravity is. No, not how it is described in physics. You will be surprised.

❝ Anybody know about the possible reasons for significant group effect...?

Chance? IMHO, testing for it is futile (see there).

---

• Unless you perform the study in cloned subjects, which would violate an assumption of the model, namely independence. If I would ever see a study with a p-value >0.05 for the subject effect it would ring my alarm bells.

—
Dif-tor heh smusma 🖖🏼 Довге життя Україна! 
Helmut Schütz


The quality of responses received is directly proportional to the quality of the question asked. 🚮
Science Quotes

Complete thread:

• Possible reasons for group effect GM 2019-07-20 07:36 [Design Issues] 
  • Group “effect”Helmut 2019-07-20 14:02
  • Possible reasons for group effect ElMaestro 2019-07-20 19:20
    • Possible reasons for group effect GM 2019-07-23 06:23
      • “Group-by-Treatment Interaction” Helmut 2019-07-23 10:32
        • “Group-by-Treatment Interaction” BEQool 2024-10-22 12:39
          • “Group-by-Treatment Interaction” Helmut 2024-10-22 12:47
            • OT: A choice between mittyri 2024-10-22 16:03
              • OT: A choice between BEQool 2024-10-23 11:02
                • OT: A choice between Helmut 2024-10-23 11:58
                  • OT: A choice between BEQool 2024-10-23 13:17
                    • OT: A choice between Helmut 2024-10-23 13:22
                    • Groups: Overlapping CIs Helmut 2024-11-03 11:36
                      • Groups: Overlapping CIs BEQool 2024-11-05 09:14
                        • Groups: Overlapping CIs Helmut 2024-11-05 10:12
                          • Groups: Overlapping CIs BEQool 2024-11-06 07:44
                            • Groups: (Hardly‽) overlapping CIs Helmut 2024-11-21 13:20
                              • Groups: (Hardly‽) overlapping CIs BEQool 2024-11-22 12:32
                                • Groups: (Hardly‽) overlapping CIs Helmut 2024-11-22 12:58
                                • Multiplicity? Helmut 2024-11-23 13:05
                                  • Groups BEQool 2024-11-26 08:15