Geoscience Reference
In-Depth Information
h e boxes have lines at the lower quartile, the median, and the upper quartile
values. h e whiskers are lines extending from each end of the boxes to show
the extent or range of the rest of the data.
h e most popular measures for dispersion are range, variance and
standard deviation. We have already used the range to dei ne the midpoints
of the classes. h e range is the dif erence between the highest and lowest
value in the data set.
range(corg)
ans =
5.1447
h e variance is the average of the squared deviation of each number from the
mean of a data set.
var(corg)
ans =
1.3595
h e standard deviation is the square root of the variance.
std(corg)
ans =
1.1660
Note that, by default, the functions
var
and
std
calculate the sample variance
and sample standard deviation providing an unbiased estimate of the
dispersion of the population. When using
skewness
to describe the shape of
the distribution, we observe a slightly negative skew.
skewness(corg)
ans =
-0.2529
Finally, the peakedness of the distribution is described by the kurtosis. h e
result from the function
kurtosis
,
kurtosis(corg)
ans =
2.4670
suggests that our distribution is slightly l atter than a Gaussian distribution
since its kurtosis is less than three.
