[LTER-im] measurmentScale/precision - what definition? howtohandle?

[Tim Bergsma]

Right.  I think what Matt means by "two attributes" is what I meant by
"split the table".

Matt Jones wrote:
> 
> A short note on Barbara's two-fish-scales problem.  This really begs the
> question "what is an attribute?".  I have always felt that an attribute
> within a table should contain a set of values that can be analyzed
> uniformly because they were measured using the same methods and
> conditions.  Barbara's example shows that some of her attributes
> represent measurements that were taken using different methods, and even
> different instruments.  Thus, one might expect that the precision (and
> other attribute properties) for her measurements is not constant, and
> that some analyses may be sensitive to her different methods.
> 
> Personally, I think the right thing in this case is to represent this
> data as two separate attributes, each of which uses a homogeneous set of
> methods and instruments.  If someone wants to combine the two attributes
> together for a particular analysis, they can inspect the attribute
> metadata (e.g., precision), and determine if it would be acceptable for
> their particular analysis.  Combining the measurements using different
> methods together a priori gives the impression that they are homogeneous
> and appropriate for all analytical purposes, which is clearly not the
> case here.
> 
> Of course, this is probably inconvenient for the investigators who
> collected the data and know it well.  They probably understand the
> limitations of the data and have a sense of the differences in precision
> among the values.  But, when representing the data for external
> consumption (e.g., through EML and the web), it would probably be better
> to be explicit about these details.
> 
> Matt
> 
> Tim Bergsma wrote:
> > P.S.  This doesn't solve Barbara's two-fish-scales problem.  Alas!  I
> > fear it is unsolvable.  Perhaps she should just report the worst of the
> > two relevant precisions, or split the table.
> 
> --
> -------------------------------------------------------------------
> Matt Jones                                     jones at nceas.ucsb.edu
> http://www.nceas.ucsb.edu/    Fax: 425-920-2439    Ph: 907-789-0496
> National Center for Ecological Analysis and Synthesis (NCEAS)
> University of California Santa Barbara
> Interested in ecological informatics? http://www.ecoinformatics.org
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-- 
Tim Bergsma
LTER Information Manager
W.K. Kellogg Biological Station
Michigan State University
Hickory Corners, MI   49060
269/671-2337
tbergsma at kbs.msu.edu
http://lter.kbs.msu.edu