[R-sig-ME] Comparison of 2 treatments

[Ben Bolker]

On 14-04-30 05:44 AM, Hamada Elsayed Ali wrote:
> Dear All,

> I'd like for your help as I have a sediment data collected before,
> within and after the field margin and my data looks like that:

> Site sediment   position   management      slope
> 
> 1    15.20      before     managed         steep
> 1    10.10      within     managed         steep
> 1    11.20      after      managed         steep
> 2    14.20      before     natural         steep
> 2    12.10      within     natural         steep
> 2    13.20      after      natural         steep
> 3    8.20       before     managed         flat
> 3    11.10      within     managed         flat
> 3    14.20      after      managed         flat
> 4    16.20      before     natural         flat
> 4    12.10      within     natural         flat
> 4    10.20      after      natural         flat

> I'd like to compare the sediment before and after in the management
> and slope and to know how much the sediment reduction or the
> increasing in the different treatments.  Can anybody help me in such
> a question.  Thanks,

  Is this all of your data or a subset?

  What have you tried?  Have you read any literature on mixed models
(e.g. Pinheiro and Bates's 2000 book, or Gelman and Hill 2008,
or one of Zuur et al's books)?  Do you know/can you express
what model you would fit if there were no random effects involved?

  Ben Bolker