Organohalogen concentrations and a gross and histologic ...

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3.1.1 Normality
Basic statistics for the 14 FA traits are shown in Table 3. Deviation from normality
could be detected in 12 of the 14 traits (Table 4). To further investigate
the deviations from normality the data was analysed for skewness and kurtosis
(Table 4). Asymmetric distributions (skewness) could be significantly detected
in 3 traits; two traits (29 and 32) were skewed to the right and one trait
(28) was skewed to the left side. Kurtosis were found significant in 11 traits,
and in all cases the distribution was leptokurtic (a distribution having many
values around the mean and in the “tails”, far from the mean) (Table 4). The 3
significant traits from test for skewness showed divergent and no consisting
left-right trends against a single side. As the assumption of normality of the
data in several cases could be doubted, both parametric and non-parametric
statistical tests were performed in further analysis.
Table 3
Basic statistics (millimeter) of the 14 metric bilateral traits used to detect fluctuating asymmetry
in polar bear skulls (n=289) 1892-2002. L: left; R: right; SD: Standard Deviation; n=count.
Trait/statistics Mean ± SD Min-Max n
L R L R
Skull
21 110.4 ± 14.8 110.3 ± 13.9 21-154.3 68.4-154.6 247
22 26.4 ± 2.7 26.3 ± 2.6 18.3-33.5 18.4-34.9 260
24 58 ± 4.6 58.4 ± 4.2 24-67.1 29.3-66.9 259
25 325.6 ± 38.8 326.3 ± 33.3 25-392 210-391 227
28 166.9 ± 18.9 167.6 ± 16.9 28-207.5 110-207 268
29 19.2 ± 1.3 19.2 ± 1.1 12.3-29.0 12.4-21.6 275
30 25.5 ± 2.5 25.7 ± 2.5 12.9-30.4 13.9-30.9 274
31
Lower jaw
15.2 ± 1.8 15.0 ± 1.5 12.5-31.0 11.9-25.9 260
33 19.6 ± 1.5 19.6 ± 1.3 13.4-33.0 13.7-28.3 266
34 14.9 ± 1.9 14.8 ± 1.5 11.0-34.0 10.3-18.4 230
35 12.5 ± 1.8 12.6 ± 1.0 10.5-35.0 10.8-21.5 252
36 20.5 ± 1.6 20.4 ± 1.2 11.9-36.0 11.9-23.1 249
37 217.5 ± 24.8 217.6 ± 21.6 154.7-266.2 154.4-264.3 244
38 89.0 ±1 2.8 89.3 ± 12.3 56.6-115.1 56.1-116.5 240
3.1.2 Size dependency
In trait 25, 31 and 38 statistically significant size dependency (L-R increases by
skull size) could be detected and for trait 30, the regression showed significant
level just above 5% and the Spearman correlation a level just below 5% (Table
4). When normalising for size, this dependency disappeared for trait 25 and
partly for 38 but not 30 and 31 and therefore it was decided to work with size
normalised FA (L-R/(L/2+R/2)) in case of trait 25 and 38 in the further analysis.