2.6. Overall grading
Pearls from P. margaritifera are normally graded into four categories
that account for both quantitatively (i.e. size) and qualitatively (i.e. lustre,
surface perfection and colour) assessed characteristics as outlined in
Table 2. Overall proportions of pearls from the first and second graft
within the different grades were then compared.
2.7. Statistical analysis
Categories within four pearl quality assessment criteria (shape, size,
lustre and overall grade)were assigned different scoreswhere ‘1’ represented
the lowest grade, and increasingly higher scores were assigned
to superior grades within each criterion, depending on the number of
levels within each. For example, ‘shape’ was assessed from the lowest
grade of ‘1’ to a high of ‘6’, ‘size’ was assessed from ‘1’ to ‘5’, ‘lustre’
from ‘1’ to ‘3’ and overall pearl grade from ‘1’ to ‘5’. Normality tests
were carried out to confirm that data were not normally distributed
and Chi-square tests for Independence were used to determine if
there were significant differences in the number of pearls in each assessment
criterion (shape, size, lustre and overall grade) after first and
second graft. The same testwas also used to detectwhether the number
of pearls with circles differed significantly after first and second graft.
The testswere carried out using the IBMSPSS Ver. 20 statistical software
and values were considered significant when p b 0.05.