ANOVA Output
Dear Katrina, The F-value are different because you test different hypotheses since anova yields Type I SS. It looks like you expect Type III SS. HTH, Thierry ------------------------------------------------------------------------ ---- ir. Thierry Onkelinx Instituut voor natuur- en bosonderzoek / Research Institute for Nature and Forest Cel biometrie, methodologie en kwaliteitszorg / Section biometrics, methodology and quality assurance Gaverstraat 4 9500 Geraardsbergen Belgium tel. + 32 54/436 185 Thierry.Onkelinx at inbo.be www.inbo.be To call in the statistician after the experiment is done may be no more than asking him to perform a post-mortem examination: he may be able to say what the experiment died of. ~ Sir Ronald Aylmer Fisher The plural of anecdote is not data. ~ Roger Brinner The combination of some data and an aching desire for an answer does not ensure that a reasonable answer can be extracted from a given body of data. ~ John Tukey -----Oorspronkelijk bericht----- Van: r-sig-ecology-bounces at r-project.org [mailto:r-sig-ecology-bounces at r-project.org] Namens Katrina W. Chu Verzonden: woensdag 12 november 2008 22:27 Aan: r-sig-ecology at r-project.org Onderwerp: [R-sig-eco] ANOVA Output I have a question about my R-output when I run a three-way ANOVA. I just plugged in the interaction term into the formula and presto! ANOVA! But I noticed that if I change the order of the formula (or interaction term), I get slightly different ANOVA outputs. I've pasted the output at the bottom of this message. I didn't think that this should happen, so I would appreciate if anyone had any feedback on this problem. Thanks in advance, Kat.
ANOVA <- aov(Chlorophyll.a~Treatment*SamplingPeriod*Site) summary(ANOVA)
Df Sum Sq Mean Sq F value Pr(>F) Treatment 3 356.5 118.8 4.2878 0.005276 ** SamplingPeriod 3 374.7 124.9 4.5069 0.003911 ** Site 1 1016.5 1016.5 36.6791 2.629e-09 *** Treatment:SamplingPeriod 9 467.6 52.0 1.8747 0.053284 . Treatment:Site 3 167.8 55.9 2.0176 0.110424 SamplingPeriod:Site 3 1670.2 556.7 20.0884 2.383e-12 *** Treatment:SamplingPeriod:Site 9 277.2 30.8 1.1115 0.352455 Residuals 534 14799.5 27.7 --- Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
ANOVA <- aov(Chlorophyll.a~SamplingPeriod*Treatment*Site) summary(ANOVA)
Df Sum Sq Mean Sq F value Pr(>F) SamplingPeriod 3 369.5 123.2 4.4437 0.004264 ** Treatment 3 361.8 120.6 4.3510 0.004840 ** Site 1 1016.5 1016.5 36.6791 2.629e-09 *** SamplingPeriod:Treatment 9 467.6 52.0 1.8747 0.053284 . SamplingPeriod:Site 3 1662.0 554.0 19.9894 2.718e-12 *** Treatment:Site 3 176.0 58.7 2.1166 0.097111 . SamplingPeriod:Treatment:Site 9 277.2 30.8 1.1115 0.352455 Residuals 534 14799.5 27.7 --- Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
ANOVA <- aov(Chlorophyll.a~Site*SamplingPeriod*Treatment) summary(ANOVA)
Df Sum Sq Mean Sq F value Pr(>F) Site 1 1008.9 1008.9 36.4050 2.998e-09 *** SamplingPeriod 3 374.1 124.7 4.4990 0.003953 ** Treatment 3 364.8 121.6 4.3871 0.004607 ** Site:SamplingPeriod 3 1654.8 551.6 19.9026 3.050e-12 *** Site:Treatment 3 172.6 57.5 2.0761 0.102364 SamplingPeriod:Treatment 9 478.2 53.1 1.9172 0.047282 * Site:SamplingPeriod:Treatment 9 277.2 30.8 1.1115 0.352455 Residuals 534 14799.5 27.7 --- Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
Katrina W. Chu, H.B.Sc. M.Sc. Candidate Canadian Rivers Institute University of New Brunswick 10 Bailey Drive Fredericton, NB, E3B 6E1 E-mail: katrina.chu at unb.ca _______________________________________________ R-sig-ecology mailing list R-sig-ecology at r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-ecology Dit bericht en eventuele bijlagen geven enkel de visie van de schrijver weer en binden het INBO onder geen enkel beding, zolang dit bericht niet bevestigd is door een geldig ondertekend document. The views expressed in this message and any annex are purely those of the writer and may not be regarded as stating an official position of INBO, as long as the message is not confirmed by a duly signed document.