[R-sig-ME] nested effects for only a small subset of situations
chatfield at alumni.rice.edu
Fri Apr 21 01:11:13 CEST 2017
I am estimating a model for fire emissions factors (slopes wrt x)
spectype.lmer <- lmer( y ~ x + 1 + (x - 1 | species.type) + ( 1 | id) , data=first.long.dat )
where y actually represents a variety of (chemical) species, alll normalized by mean,
but there can be variations from one observati on to the next among a few (6) different fire-types
“type.” So I have oonxtructed the compound factor species.type as commonly described
in Bates’s writings.
id is just the sequential number of the observation of all 10 species.
Now it turns out that for two of the species, there should be an extra term somthing
like ( 1 | plume )
spectype.plume.lmer <- lmer( y ~ x + 1 + (x - 1 | species.type) + ( 1 | id) + ( 1 | plume ) , data=first.long.dat )
where all the observations with id in that plume (3 to 40 ids per plume) should have the same value.
id is nested withiin plume .
A dditionally, the intercept should depend only on species, not species.type
Only 2/10s of the observations require this value.
I want to “horde” degrees of freedom except for maybe some experimental tests to
see if the other species . Variance explained is pretty good even without including
This does not seem to fit wtihin the formula choices as I understand them.
(1) Can I create a factor CO.plume.offset which “activates” only when species is CO but
varies by plume, a level for each plume ? (allso a factor CH4. plume. offset )
(2) How about estimating the offset after spec.type.lmer is calculated using the
residuals. Then I could re-enter the offsets in a second lmer calculation, by adjusting y . This does
seem to reduce the meaning of statistical tests, but it’s very simple. The residuals for CO and CH4 for
spectype.lmer are not high but the residuals corresponding to CH4 especially do seem
to move up and down from plume to plume.
Robert.B.Chatfield at nasa.gov <mailto:Robert.B.Chatfield at nasa.gov>
Earth Science, Atmospherics, NASA Ames
Moffett Field CA 94035-1000 USA
660-604-5490 Cell: 650-793-5227
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