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Symmetry
Distribution is symmetric if its left half forms a mirror image of its right half.
-4 -3 -2 -1 0 1 2 3 4
Symmetric U shaped
10 20 30 40 50
Skewness
Skewness is a measure of a distribution's symmetry. The mode of a distribution is its highest point. If the tail on one side
of the mode is fatter or longer than the tail on the other, the distribution is skewed, i.e., it is asymmetrical.
A distribution that is not symmetric has values that tend to be more spread out on one side of the graph than on the
other. In such a case, we say that the distribution is skewed. There are three types of distributions which are left-skewed
distribution, right-skewed distribution and symmetry distribution.
Left-skewed Right-skewed Symmetric
Outliers Outliers
at low at high
values values
Mean Mode Mean Mode Mode = Mean = Median
Median Median
Let’s observe how these distributions look when you use histograms.
Left-skewed Distribution
A negative skew in an asymmetrical distribution where the tail on the left side is longer than the tail on the right is known
as left-skewed distribution. It is also called negative-skewed. In left-skewed distribution, the values are more spread out
on the left side. The median and mean are less than the mode.
Data Analysis (Computational Thinking) 257

