Fig. 7. Representative scanning electron microscope images of polished sections for (a c) accepted and (d f) rejected samples in paleointensity determination.
Fig. 4. Representative Arai plots of rejected samples from (a c) the lava flows and (d) the massive basalts observed in the IZZI experiment.
Of the rejected samples, 11 samples failed to meet criteria 3 (Fig. 3(c)), 5 samples failed to meet criteria 1 (Fig. 3(d)), and 9 samples failed to meet criteria 2 (Fig. 3 e)).
In this study, the critical criteria for paleointensity determination are q and CKerror since ~82% (258 samples) and ~71% (222 samples) of the rejected samples show q < 10 and CKerror > 5%, respectively.
For the rejected samples from the lava flows, the iron oxides are characterized by secondary precipitation forming rims of iron oxide surrounding iron-rich silicate minerals (e.g., olivine) with overall grain sizes of ~20 μm (Fig. 7 d)).
The laboratory rejected samples with incomplete documentation.
The approximation only affects sampling efficiency, not accuracy: the poorer the approximation, the larger the proportion of rejected samples.
On the other hand, specificity measures the proportion of the number of correctly rejected samples compared to the whole number of rejected samples (correctly versus incorrectly) and is calculated as follows: 12 where TN is the number of correctly rejected (true negative) samples while FP is the number of incorrectly accepted samples (false positive).
Sensitivity measures the proportion of correctly classified proteins compared to the whole number of samples which are classified as correct (correct versus incorrect) and is calculated as follows: 11 where TP is the number of correctly identified (true positive) samples, while FN is the number of incorrectly rejected samples (false negative).
A pre-specified incoherence threshold (E thresh; measured in degrees of separation between the DOAs) is used to reject sample window sets.
Moreover, an exhaustive examination of the data was carried out to reject sample plots on which illegal logging had been detected to make sure that the reduction in number of trees observed were due to natural mortality.
