I am learning R, and although I have looked in the documentation, I may be asking something obvious. Sorry, if that is the case. In a split-plot design if there is a missing subunit summary gives me a table with two rows for the same factor, one in the error within section and one in the section using error between units. With no data missing the table is "normal". How does one interpret the table when data is missing?, or is it that aov cannot cope with missing values in this case? Thanks in advance for any help. Pedro. The model I am using is of the form "y ~ A * B * C + block + Error(A/B)", I tried the simpler model "y ~ A * B + block + Error(A)" with the same result. The behaviour is the same in Version 1.1.1 and Version 1.2.0 Under development (unstable) (2000-10-11). If it matters, I am using Windows. -- ============================================================== Pedro J. Aphalo University of Joensuu Faculty of Forestry P.O. Box 111, FIN-80101 Joensuu, FINLAND mailto:pedro.aphalo at joensuu.fi http://cc.joensuu.fi/~aphalo/pedro.html fax: +358 13 251 4444 tel: +358 13 251 4406 ,,,^..^,,, ===============================================================-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
> Date: Fri, 03 Nov 2000 16:10:54 +0200 > From: "Pedro J. Aphalo" <pedro.aphalo at joensuu.fi> > > I am learning R, and although I have looked in the documentation, I may > be asking something obvious. Sorry, if that is the case.(No, the problem is with your expectations from the theory.)> In a split-plot design if there is a missing subunit summary gives me a > table with two rows for the same factor, one in the error within section > and one in the section using error between units. With no data missing > the table is "normal". How does one interpret the table when data is > missing?, or is it that aov cannot cope with missing values in this > case?aov() does cope, but the conventional analysis is indeed as you describe. Factors do have effects in more than one stratum. For example, consider the oats example in Venables & Ripley (1999). If I omit observation 70, I get> summary(oats.aov)Error: B Df Sum of Sq Mean Sq F Value Pr(F) Nf 1 841.89 841.890 0.2242563 0.6605042 Residuals 4 15016.57 3754.142 Error: V %in% B Df Sum of Sq Mean Sq F Value Pr(F) Nf 1 1100.458 1100.458 1.747539 0.2187982 V 2 1156.821 578.410 0.918521 0.4335036 Residuals 9 5667.471 629.719 Error: Within Df Sum of Sq Mean Sq F Value Pr(F) Nf 3 19921.29 6640.431 37.23252 0.0000000 Nf:V 6 408.96 68.160 0.38217 0.8864622 Residuals 44 7847.41 178.350 so Nf appears in all three strata, not just the last one. The `recovery of intra-block information is needed'. If you have an unbalanced layout (e.g. with a missing value) use lme to fit a model. V&R do this example in lme too. -- Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272860 (secr) Oxford OX1 3TG, UK Fax: +44 1865 272595 -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
"Pedro J. Aphalo" <pedro.aphalo at joensuu.fi> writes:> I am learning R, and although I have looked in the documentation, I may > be asking something obvious. Sorry, if that is the case. > > In a split-plot design if there is a missing subunit summary gives me a > table with two rows for the same factor, one in the error within section > and one in the section using error between units. With no data missing > the table is "normal". How does one interpret the table when data is > missing?, or is it that aov cannot cope with missing values in this > case? > > Thanks in advance for any help. > > Pedro. > > The model I am using is of the form "y ~ A * B * C + block + > Error(A/B)", I tried the simpler model "y ~ A * B + block + Error(A)" > with the same result.As a general matter, the theory for these designs is based on having balanced data. The analysis with aov is based on an orthogonal decompostion according to the error terms, which in the balanced case means splitting into averages and differences of the values within a plot. If each plot has received the same treatments, then there is no information in the averages of the effect of treatment (and therefore it does not appear in the between-unit stratum), but there will be if the plots have received different sets of treatment. This will be the case if some plots have missing values, but not only that: The error model also becomes dubious (it essentially implies that averages have the same variance no matter how many observations they are averages of). -- O__ ---- Peter Dalgaard Blegdamsvej 3 c/ /'_ --- Dept. of Biostatistics 2200 Cph. N (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907 -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._