[R-sig-ME] Variance components questions
Thierry.ONKELINX at inbo.be
Tue Feb 22 16:13:17 CET 2011
I assume that the samples are reference samples with known concentration? In that case I would create a new variable: logRatio = log(measurement/known) and model that as logRatio ~ operator + (1|day/run) + (1|sample). This new variable is the relative bias of the measurements.
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek
team Biometrie & Kwaliteitszorg
Research Institute for Nature and Forest
team Biometrics & Quality Assurance
tel. + 32 54/436 185
Thierry.Onkelinx at inbo.be
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
> -----Oorspronkelijk bericht-----
> Van: r-sig-mixed-models-bounces at r-project.org
> [mailto:r-sig-mixed-models-bounces at r-project.org] Namens Karim Lounes
> Verzonden: dinsdag 22 februari 2011 0:01
> Aan: r-sig-mixed-models at r-project.org
> Onderwerp: [R-sig-ME] Variance components questions
> Hi All,
> I am a biochemist with limited background in statistics, so
> please forgive the naivety of my question.
> I am interested in estimating the precision of a measurement
> system and the variance components of three factors.
> This is how the experiment was designed: 5 samples, each
> considered a level were measured. Each sample was measured
> twice a day (run) for 10 days (days) by two different
> operators (operator). Each measurement was replicated 3
> times. The factor (days) is not continuous as the goal was to
> generalize the estimation of the precision of the measurement
> system for all days.
> I have read a number of posts on this list and also read Mr.
> bates online book of lem4.
> >From what I understood the model would be a crossed design
> and I run
> following analysis:
> Measurement ~ samples + (1|days) + (1|run) +(1|operator)
> Is this model appropriate? and is there a way to gauge the
> precision of the the estimates of the variance components by
> a confidence interval?
> Thank you for your help
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