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From |
"Lachenbruch, Peter" <[email protected]> |

To |
"'[email protected]'" <[email protected]> |

Subject |
st: RE: R: choice of ANOVA for an ecological experiment |

Date |
Tue, 1 Feb 2011 08:12:09 -0800 |

One reason might be that MANOVA is notoriously sensitive to non-normality. The number of individuals remaining is likely not to be normal, weight might be, not sure about size - is it height or body volume or something else? At any rate, one might compute a permutation test on T-squared values to get a valid test. Tony Peter A. Lachenbruch Department of Public Health Oregon State University Corvallis, OR 97330 Phone: 541-737-3832 FAX: 541-737-4001 -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Carlo Lazzaro Sent: Monday, January 31, 2011 12:17 AM To: [email protected] Cc: 'Jacob Felson' Subject: st: R: choice of ANOVA for an ecological experiment Jacob wrote: "The outcome variables include the number of individuals remaining, the weight of the individuals remaining, and the size of the individuals remaining." Just out of curiosity: why, with three outcomes, don't you consider a MANOVA (see - help manova - in Stata 9/2 SE)? Kind Regards, Carlo -----Messaggio originale----- Da: [email protected] [mailto:[email protected]] Per conto di Jacob Felson Inviato: domenica 30 gennaio 2011 21.00 A: [email protected] Oggetto: st: choice of ANOVA for an ecological experiment Hello, I am wondering whether anyone might be able to advise me about the best choice of ANOVA to analyze the results of an ecological experiment. In each of eight ponds, a certain number of various species were put into enclosures that were randomly assigned to a set of four predator conditions. The four randomly assigned predator conditions were: no predators, 8 predators, 16 predators, and 24 predators. Each predator condition was assigned to 3 replicates. So the total number of enclosures was: 8 ponds x 4 predator conditions x 3 replicates = 96. The outcome variables include the number of individuals remaining, the weight of the individuals remaining, and the size of the individuals remaining. This experiment appears to follow a split-plot design. Is this correct? That is, the error of the pond effect is distinct from the error of the predator condition effect. The sum of squared error for the pond would be equal to the sum of squares for the predator condition. The sum of squared error for the predator condition would be equal to the residual sum of squares. The predator condition variable is called density, and the outcome variable is number of survivors. If all of this is accurate, then I'm guessing that a simple model might be: anova survivors pond / density | pond / Is this correct? One further issue is that the ponds are fixed, not random. Unlike the textbook split-plot design, a whole-plot has not been randomly assigned to ponds. Instead, there are simply 8 ponds, within each of which individuals were collected and placed in enclosures with varying predator conditions. I would very much appreciate help on this issue! Sincerely, Jacob Felson * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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