Hi all, Firstly excuse-me by this off-topic question. I'm very confused to decide what is the better analysis to use. Whem the experiments is a tradicional design of manipulative experiments, it is easy to decide. But in natural observations is too complicated. I have 6 farms, each farm cultives some sugarcane's varieties (maybe or not the same varieties by farm). For each farm I make 3 transects (lines) (replicates) crossing all varieties, and I make one collect point in each variety. Example: In farm "A" I have 3 varieties and I make 3 transect, so I have 3*3 = 9 points. In each collect point all data are obtained independently. The data are: * production (my response) My explanatory variables are: * sugarcane's variety (categorical, not necessarily the same on all farms) * age of sugarcane (continuous, not necessarily the same on all farms) * name of farm (block ??) * topography (categorical, not necessarily the same on all farms) * infestation (continuous, the main explanatory variable) I think make a modelo like this: lm(production~variety*age*farm*topography*infestation) My doubt is about the errors, I dont get to know if this is nested, mixed etc. Anybody can help-me. Thanks for all Ronaldo -- Short people get rained on last. -- | //|\\ [*****************************][*******************] || ( ? ? ) [Ronaldo Reis J?nior ][PentiumIII-600 ] | V [ESALQ/USP-Entomologia, CP-09 ][HD: 30 + 10 Gb ] || / l \ [13418-900 Piracicaba - SP ][RAM: 128 Mb ] | /(lin)\ [Fone: 19-429-4199 r.229 ][Video: SiS620-8Mb ] ||/(linux)\ [chrysopa at insecta.ufv.br ][Modem: Pctel-onboar] |/ (linux) \[ICQ#: 5692561 ][Kernel: 2.4.18 ] || ( x ) [*****************************][*******************] ||| _/ \_Powered by Gnu/Debian Woody D+:) | Lxuser#: 205366