I don't think you are clear enough about the layout within each block. If the four treatments are randomized, I would choose the first model.
KW On Tue, Jul 21, 2009 at 9:38 AM, Jean-Paul Maalouf < jean-paul.maal...@u-bordeaux1.fr> wrote: > Hello, > > I would be very grateful if someone could give me a hand with my split plot > design problems. > > So here is my design : > I am studying the crossed-effects of water (wet/dry) and mowing > (mowed/not-mowed = nm) on plant height (PH) within 2 types of plant > communities (Xerobromion and Mesobromion) : > - Within each type of communities, I have localised 4 blocks > - In each block, I have defined 4 plots in order to have the 4 possible > treatments of both the water and mowing factors : nm/dry ; mowed/dry ; > mowed/wet ; nm/wet. > > Here is my data table : > > Community Block Mowing Water PH > 1 Meso b1 Mowed Wet 7.40 > 2 Meso b1 nm Wet 13.10 > 3 Meso b1 Mowed Dry 5.55 > 4 Meso b1 nm Dry 10.35 > 5 Meso b2 nm Dry 10.70 > 6 Meso b2 Mowed Dry 6.38 > 7 Meso b2 nm Wet 9.75 > 8 Meso b2 Mowed Wet 6.35 > 9 Meso b3 nm Wet 9.60 > 10 Meso b3 Mowed Dry 5.10 > 11 Meso b3 nm Dry 10.05 > 12 Meso b3 Mowed Wet 6.25 > 13 Meso b4 nm Wet 9.00 > 14 Meso b4 Mowed Wet 6.50 > 15 Meso b4 nm Dry 7.75 > 16 Meso b4 Mowed Dry 5.90 > 17 Xero b5 nm Wet 7.69 > 18 Xero b5 Mowed Wet 8.11 > 19 Xero b5 nm Dry 3.98 > 20 Xero b5 Mowed Dry 3.69 > 21 Xero b6 nm Wet 5.24 > 22 Xero b6 Mowed Wet 4.22 > 23 Xero b6 nm Dry 6.55 > 24 Xero b6 Mowed Dry 4.40 > 25 Xero b7 Mowed Dry 3.79 > 26 Xero b7 nm Dry 3.91 > 27 Xero b7 nm Wet 9.00 > 28 Xero b7 Mowed Wet 8.50 > 29 Xero b8 Mowed Dry 3.33 > 30 Xero b8 nm Wet 6.25 > 31 Xero b8 Mowed Wet 8.00 > 32 Xero b8 nm Dry 6.33 > > I actually have 2 questions : > I wrote my model in two different ways, and there were differences in > P-Values according to the model written : > > First model : summary(aov(PH~Community*Mowing*Water + Error(Block))) > Error: Block > Df Sum Sq Mean Sq F value Pr(>F) > Community 1 42.182 42.182 24.407 0.002603 ** > Residuals 6 10.370 1.728 > --- > Signif. codes: 0 ?***? 0.001 ?**? 0.01 ?*? 0.05 ?.? 0.1 ? ? 1 > > Error: Within > Df Sum Sq Mean Sq F value Pr(>F) > Mowing 1 40.007 40.007 21.1747 0.0002215 *** > Water 1 23.120 23.120 12.2370 0.0025673 ** > Community:Mowing 1 21.060 21.060 11.1467 0.0036554 ** > Community:Water 1 6.901 6.901 3.6524 0.0720478 . > Mowing:Water 1 1.611 1.611 0.8527 0.3680090 > Community:Mowing:Water 1 0.858 0.858 0.4542 0.5089331 > Residuals 18 34.008 1.889 > --- > > - Second model (assuming that Mowing*Water are nested inside the Block > factor) : > summary(aov(PH~Community*Mowing*Water + Error(Block/(Mowing*Water)))) > > Error: Block > Df Sum Sq Mean Sq F value Pr(>F) > Community 1 42.182 42.182 24.407 0.002603 ** > Residuals 6 10.370 1.728 > --- > Signif. codes: 0 ?***? 0.001 ?**? 0.01 ?*? 0.05 ?.? 0.1 ? ? 1 > > Error: Block:Mowing > Df Sum Sq Mean Sq F value Pr(>F) > Mowing 1 40.007 40.007 37.791 0.0008489 *** > Community:Mowing 1 21.060 21.060 19.893 0.0042820 ** > Residuals 6 6.352 1.059 > --- > Signif. codes: 0 ?***? 0.001 ?**? 0.01 ?*? 0.05 ?.? 0.1 ? ? 1 > > Error: Block:Water > Df Sum Sq Mean Sq F value Pr(>F) > Water 1 23.1200 23.1200 6.0725 0.04884 * > Community:Water 1 6.9006 6.9006 1.8125 0.22685 > Residuals 6 22.8439 3.8073 > --- > Signif. codes: 0 ?***? 0.001 ?**? 0.01 ?*? 0.05 ?.? 0.1 ? ? 1 > > Error: Block:Mowing:Water > Df Sum Sq Mean Sq F value Pr(>F) > Mowing:Water 1 1.6110 1.6110 2.0085 0.2062 > Community:Mowing:Water 1 0.8581 0.8581 1.0697 0.3409 > Residuals 6 4.8126 0.8021 > > Both models give me interesting (but different!) results. Which one would > be the most appropriate? > > Second question : How can I verify preliminary assumptions (normality of > residuals and variance homogeneity) in this kind of models? > When I ask R to extract residuals, the answer is "NULL": > > residuals(aov(PH~Community*Mowing*Water + Error(Block/(Mowing*Water)))) >> > NULL > >> residuals(aov(PH~Community*Mowing*Water + Error(Block))) >> > NULL > > A huge thanks to the one who will rescue (or at least try to rescue) my > PhD! > > Sincerely, > > > -- > Jean-Paul Maalouf > UMR 1202 BIOGECO > Inra - Université Bordeaux 1 > Bâtiment B8, Avenue des Facultés > 33405 Talence, France > Tel : 05 40008772 > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > [[alternative HTML version deleted]]
______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
