[R] Balanced design, differences in results using anova and lmer/anova

[Rolf Turner]

Not sure --- never sure with this stuff! :-) --- but I think that  
your problem
might be (at least in part) that the coding for block is repeated within
each location.  Block 1 in location 1 is *not* the same as block 1 in  
location 2;
this is what nesting in effect means.  The structure of lmer()  
requires that
this be acknowledged explicitly.  You have a total of 8 blocks ---  
four in location 1
and four in location 2.  Code them as 1, ..., 8 and not as 1, ..., 4  
repeated.

Give this a go and see if it helps.

	cheers,

		Rolf Turner

On 27/02/2009, at 10:06 PM, Lars Kunert wrote:

> Hi, I am trying to do an analysis of variance for an unbalanced  
> design.
> As a toy example, I use a dataset presented by K. Hinkelmann and O.
> Kempthorne in "Design and Anaylysis of Experiments" (p353-356).
> This example is very similar to my own dataset, with one  
> difference: it
> is balanced.
> Thus it is possible to do an anaylsis using both: (1) anova, and  
> (2) lmer.
> Furthermore, I can compare my results with the results presented in  
> the
> book (the book uses SAS).
>
> In short:
>> using anova, I can reproduce the results presented in the book.
>> using lmer, I fail to reproduce the results
> However, for my "real" analysis, I need lmer - what do I do wrong?
>
> The example uses as randomized complete block desigh (RCBD) with a
> nested blocking structure
> and subsampling.
>
> response:
>   height (of some trees)
> covariates:
>   HSF (type of the trees)
> nested covariates:
>   loc (location)
>   block  (block is nested in location)
>
> # the data (file: pine.txt) looks like this:
>
> loc    block    HSF    height
> 1    1    1    210
> 1    1    1    221
> 1    1    2    252
> 1    1    2    260
> 1    1    3    197
> 1    1    3    190
> 1    2    1    222
> 1    2    1    214
> 1    2    2    265
> 1    2    2    271
> 1    2    3    201
> 1    2    3    210
> 1    3    1    220
> 1    3    1    225
> 1    3    2    271
> 1    3    2    277
> 1    3    3    205
> 1    3    3    204
> 1    4    1    224
> 1    4    1    231
> 1    4    2    270
> 1    4    2    283
> 1    4    3    211
> 1    4    3    216
> 2    1    1    178
> 2    1    1    175
> 2    1    2    191
> 2    1    2    193
> 2    1    3    182
> 2    1    3    179
> 2    2    1    180
> 2    2    1    184
> 2    2    2    198
> 2    2    2    201
> 2    2    3    183
> 2    2    3    190
> 2    3    1    189
> 2    3    1    183
> 2    3    2    200
> 2    3    2    195
> 2    3    3    197
> 2    3    3    205
> 2    4    1    184
> 2    4    1    192
> 2    4    2    197
> 2    4    2    204
> 2    4    3    192
> 2    4    3    190
>
> #
> # then I load the data
> #
> read.data = function()
> {
> 	d = read.table( "pines.txt", header=TRUE )
>
> 	d$loc       = as.factor( d$loc   )
> 	d$block.tmp = as.factor( d$block )
> 	d$block     = ( d$loc:d$block.tmp )[drop=TRUE]  # lme4 does not  
> support
> implicit nesting
>
> 	d$HSF   = as.factor( d$HSF )
>
> 	return( d )
> }
>
> d = read.data()
>
>
> #
> # using anova.....
> #
> m.aov = aov( height ~ HSF*loc + Error(loc/block + HSF:loc/block),  
> data=d )
> summary( m.aov )
>
> #
> # I get:
> #
> Error: loc
>     Df Sum Sq Mean Sq
> loc  1  20336   20336
>
> Error: loc:block
>           Df  Sum Sq Mean Sq F value Pr(>F)
> Residuals  6 1462.33  243.72
>
> Error: loc:HSF
>         Df  Sum Sq Mean Sq
> HSF      2 12170.7  6085.3
> HSF:loc  2  6511.2  3255.6
>
> Error: loc:block:HSF
>           Df  Sum Sq Mean Sq F value Pr(>F)
> Residuals 12 301.167  25.097
>
> Error: Within
>           Df Sum Sq Mean Sq F value Pr(>F)
> Residuals 24 529.00   22.04
>
> #
> # which is, what I expected, however, using lmer....
> #
> m.lmer = lmer( height ~ HSF*loc + HSF*(loc|block), data=d )
> anova( m.lmer )
>
> #
> # I get:
> #
> Analysis of Variance Table
>         Df  Sum Sq Mean Sq
> HSF      2 12170.7  6085.3
> loc      1  1924.6  1924.6
> HSF:loc  2  6511.2  3255.6
>
> #
> # what is, at least not what I expected...
> #
> Thanks for your help, Lars
>
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