Helmut ★★★ Vienna, Austria, 2012-12-27 18:21 (4108 d 22:21 ago) Posting: # 9761 Views: 8,670 |
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Dear all, one of my stat-pro friends regularly mumbled “α-inflation!” when I mention imbalanced cross-overs but failed to give a concise explanation – we quickly moved to more interestic topics (NLYW etc.) instead. Is this an urban myth or not? Does anybody know a reference? Of course I could fire up some sim’s – but I don’t want to reinvent the wheel. — 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 |
ElMaestro ★★★ Denmark, 2012-12-28 10:30 (4108 d 06:11 ago) @ Helmut Posting: # 9762 Views: 7,715 |
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Hi Helmut, not sure I follow you. Although partitioning of SS is an issue, imbalance per se is not causing inflation of alpha in simple crossovers. The phenomenon has not been studied or published for 2-stage designs, though. Did you mean to say something else? — Pass or fail! ElMaestro |
Helmut ★★★ Vienna, Austria, 2012-12-28 15:37 (4108 d 01:05 ago) @ ElMaestro Posting: # 9763 Views: 7,633 |
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Hi ElMaestro, ❝ […] imbalance per se is not causing inflation of alpha in simple crossovers. Do you know that or do you assume it? ❝ The phenomenon has not been studied or published for 2-stage designs, though. Yep. Mdme Potvin: “[…] each stage was assumed to be balanced with respect to sequence.” Since I want to avoid troubles with regulators“The imbalanced case is outside the validated framework. The applicant should justify that the consumers’s risk is preserved in the actual study.” I recommend my clients to randomize the second stage in such a way that imbalance in the first stage is counteracted (e.g., stage 1 TR|RT 10|12, ntotal 32, stage 2 TR|RT 6|4).❝ Did you mean to say something else? I was just interested in common 2,2,2 cross-overs. — 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 |
ElMaestro ★★★ Denmark, 2012-12-29 09:44 (4107 d 06:58 ago) @ Helmut Posting: # 9764 Views: 7,583 |
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Hi Helmut, I am still not sure I follow you. Can you put a few more words to your post? Are we talking one-stage or two-stage designs? Imbalance has not been studied for two-stage designs. — Pass or fail! ElMaestro |
Helmut ★★★ Vienna, Austria, 2012-12-29 16:42 (4106 d 23:59 ago) @ ElMaestro Posting: # 9765 Views: 7,558 |
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Hi ElMaestro, ❝ Are we talking one-stage or two-stage designs? One stage (fixed sample 2,2,2 cross-over). Duno what to say else that I did in my original post. Is it true or not that α might be inflated in imbalanced studies? I’m not talking about nominal α (which is ≤0.05) but the one we can expect using the usual methods… If this is just a rumor, fine. If not, how large an inflation can we expect? ❝ Imbalance has not been studied for two-stage designs. Yep. BTW — 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 |
d_labes ★★★ Berlin, Germany, 2012-12-31 14:50 (4105 d 01:52 ago) @ Helmut Posting: # 9768 Views: 7,315 |
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Dear Helmut, ❝ one of my stat-pro friends regularly mumbled “α-inflation!” when I mention imbalanced cross-overs but failed to give a concise explanation – we quickly moved to more interestic topics (NLYW etc.) instead. Is this an urban myth or not? Never heard about such a theme like “α-inflation!” for imbalanced cross-overs. So I think your stat-pro friend should justify his mumbling (innocent until proven guilty - at least in under German law) before you waste computer time and energy for over-heating your machine(s). — Regards, Detlew |
d_labes ★★★ Berlin, Germany, 2013-01-09 16:23 (4096 d 00:18 ago) @ Helmut Posting: # 9803 Views: 7,520 |
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Dear Helmut, from this post I know that you are working on simulations for the 2x2x2 crossover, at least on balanced design. Do you believe the subject line? If not, have a look on the following code : # simulate 2x2x2 crossover studies with log-normal data Using these functions: require(PowerTOST) — Regards, Detlew |
Helmut ★★★ Vienna, Austria, 2013-01-09 17:10 (4095 d 23:31 ago) @ d_labes Posting: # 9805 Views: 7,077 |
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Dear Detlew! ❝ Do you believe the subject line? First: no. ❝ If not, have a look on the following code : Second: yes. Unbelievable. ❝ ❝ ❝ ❝ ❝ Amazing. With roundit=T I got 0.033605 . Same value if I switch lines 65–66 to R’s round() . With my original code I got 0.033236 (unrounded) and 0.033786 (R’s rounding), but run-time was ~30 minutes.Concerning the question at the top of your source code: I think so but I’m not sure as well. BTW, couldn’t figure out how to modify the code for imbalanced sequences. Just discovered that I’m not the first simulator. See Chapter 4.2.1 of Chow & Liu (any edition). — 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 |
d_labes ★★★ Berlin, Germany, 2013-01-09 17:56 (4095 d 22:45 ago) @ Helmut Posting: # 9806 Views: 7,116 |
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Dear Helmut! ❝ With ❝ Same value if I switch lines 65–66 to R’s Your observation that cround() and round() work equal if rounded to 4 decimals.❝ BTW, couldn’t figure out how to modify the code for imbalanced sequences. Described in the question for unbalanced designs. Based on this: power2.TOST(CV=0.3,n=c(4,7),theta0=1.25) — Regards, Detlew |
Helmut ★★★ Vienna, Austria, 2013-01-09 19:07 (4095 d 21:35 ago) @ d_labes Posting: # 9807 Views: 7,091 |
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Dear Detlew! ❝ ❝ Same value if I switch lines 65–66 to R’s ❝ Your observation that Oh no! So we can abandon the 1 mio function calls and stick to round() . ❝ power.sim2x2(CV=0.3, n=c(4,7), GMR=1.25) I see. Didn’t understand your lines 6–7. Now let’s see what I got for the extreme ’corners’ and the center of my grid. All sim’s with the same seed. Values in red are significantly >0.05… magical mystery code my code power.TOST Rounding is evil – at least if we want to compare results with expected (theoretical) ones. Extremely imbalanced sequences, where n1+n2=n from above. Arrows denote direction of the change compared to balanced cases. magical mystery code power2.TOST Can’t see any relevant α-inflation – on the contrary (see esp. power(2).TOST). I think Martin ows my a beer. THX for the code; saved me two days of sim’s. — 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 |
d_labes ★★★ Berlin, Germany, 2013-01-10 12:07 (4095 d 04:35 ago) @ Helmut Posting: # 9813 Views: 6,979 |
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Dear Helmut! ❝ Can’t see any relevant α-inflation – on the contrary (see esp. power(2).TOST). I think Martin ows my a beer. One caveat: Both power2.TOST() and the "magical mystery code" rely on the positive answer to my question in the comments above the code. To get your beer be prepared (hint: period-by-sequence means, Hauschke, Steinijans, Pigeot Chapter 3.4.2.2).❝ THX for the code; saved me two days of sim’s. How much is your daily salary? I will give you the details of my bank account . — Regards, Detlew |
Helmut ★★★ Vienna, Austria, 2013-01-10 14:45 (4095 d 01:57 ago) @ d_labes Posting: # 9815 Views: 7,112 |
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Dear Detlew! ❝ One caveat: Both Right. Beyond my capabilities. ❝ hint: period-by-sequence means, Hauschke, Steinijans, Pigeot Chapter 3.4.2.2. OK, one of the assumptions I’m comfortable with. ❝ ❝ THX for the code; saved me two days of sim’s. ❝ How much is your daily salary? I will give you the details of my bank account . Daily salary: As a one-man band no salary at all. Record honorary € 5,000.–/day, but sometimes zero for two months. I run sim’s to satisfy my own curiosity which is difficult to rate. Once I’ll be in Berlin next time beers on my bill. Edit: Talked to Martin. He apologized and will pay our beers. — 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 |