These data are from Grzegorz (Greg) Zadora at the Institute of Forensic Research in Krakow, Poland. They are the log of the ratios of each element to oxygen, so logNaO is the log(10) of the Sodium to Oxygen ratio, and logAlO is the log of the Aluminium to Oxygen ratio. The instrumental method was SEM-EDX.
data(glass)a data.frame with 2400 rows and 9 columns.
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The item indicates the object the glass came from. The levels for each item
are unique to that item. The fragment can be considered a sub-item. When
collecting these observations Greg took a glass object, say a jam jar, he
would then break it, and extract four fragments. Each fragment would be
measured three times upon different parts of that fragment. The fragment
labels are repeated, so, for example, fragment "f1" from item "s2" has
nothing whatsoever to do with fragment "f1" from item "s101".
For two level models use item as the lower level - three level models can
use the additional information from the individual fragments.
Aitken, C.G.G. Zadora, G. & Lucy, D. (2007) A Two-Level Model for Evidence Evaluation. Journal of Forensic Sciences: 52(2); 412-419.