[R-sig-ME] nested two level mixed model with lmer

Thierry Onkelinx thierry.onkelinx at inbo.be
Tue Jun 14 11:52:31 CEST 2016

Dear Christina,

m1 assumes a linear trend along days with different slopes among treatments
and replicates. Whereas m2 assumes that the linear trend along days only
depends on treatment. So all replicates within a treatment have the same

PS Don't post in HTML as it can make the text unreadable.

Best regards,

ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature and
team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance
Kliniekstraat 25
1070 Anderlecht

To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to say
what the experiment died of. ~ Sir Ronald Aylmer Fisher
The plural of anecdote is not data. ~ Roger Brinner
The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of data.
~ John Tukey

2016-06-14 11:14 GMT+02:00 Cristina Muschitiello <muschitiello op gmail.com>:

> I'd need to have a suggestion for my analysis:
> I have two soil treatments: CT and NT.
> For each treatment, I have 11 CO2 measurements taken in 7 times, i.e. 11
> "replicates" for 7 dates.
> Replicates are nested in the treatments.
> I'd like to evaluate if the measurements are different in time for the two
> treatments.
> My information are:
>    - replicates(11)=random factor;
>    - days=repeated measure factor (fixed factor)
>    - treatment = between subject factor (fixed factor)
>    - CO2 = Co2 emission measures (=dependent variable)
> Is it correct to consider this as a nested two-level repeated measures
> Is it correct to use the following R sintax?
> m1 <- lmer(CO2~days*treatment+(days|replicates),mydata)
> Is this a random intercept and slope model with replicates nested in
> treatment?
> Is it correct to say that this model accounts for:
> the main effect of treatment and time and
> the interaction between the two?
> What would be the difference of m1 from m2?
> m2 <- lmer(CO2~days*treatment+(1|replicates),mydata)
> Thank you
> Cristina
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