Hi:

Why is phase nested within sites? Shouldn't sites and phase be crossed?
After all, there is one intervention (works) that purportedly affects the
river both upstream and downstream. Moreover, why is log(flow) being treated
as both a fixed and random effect?

Just curious,
Dennis

On Wed, Sep 15, 2010 at 5:58 PM, Meissner, Tony (DFW) <
Tony.Meissner@sa.gov.au> wrote:

> I have a dataset relating the effects of engineering works on the level of
> salinity in a river before and after the works.  I have modelled this using
> linear mixed effects models to determine if the significance and level of
> the response to the works.  I am wanting to calculate the se of difference
> at several points. I am not sure of how to calculate the difference and
> which estimate of se I should be using e.g. is it the random effects or the
> fixed effects estimates and what formula to use e.g. the one for calculating
> se using linear models?
>
> To assist here is one of the models I have formulated
>
>  log(Salinity) ~ log(flow), random=~log(flow)|sites/phase
>
> where sites is a factor with levels upstream & downstream, and phase is a
> factor with two levels before and after.
>
> Any help would be appreciated.
>
> Tschüß
> Tony Meissner
> Principal Scientist - Monitoring
> Department for Water | Level 3 28 Vaughan Terrace Berri SA 5343
> T 8595 2209  | M 0401 124 971
> E tony.meissner@sa.gov.au<mailto:tony.meissner@sa.gov.au>
>
> Mon | Tue | Wed | Thurs | Fri
>
> www.waterforgood.sa.gov.au<http://www.waterforgood.sa.gov.au/> |
> www.sa.gov.au<http://www.sa.gov.au/>
>
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