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Summary Statistics

Summary statistics are employed when the variable has the numerical data

- Mean.
The sample mean
- Median.
The sample median is the value of the ``middle'' data point.
When the size is an odd number, the median is simply the middle value;
for example, the median of ``2, 4, and 7'' is 4.
When we have the data with even number of the size,
the median is the mean of the two middle values.
Thus, the median of the numbers ``2, 4, 7, 12'' is (4+7)/2 = 5.5.
The sample median is known to be
less affected by exterme measurements in comparison to the mean.
- Standard deviation (S.D.).
The sample variance.
The coefficient of variation (CV)

CVcan be used to compare the variability in a different unit of measurement. - Lower and upper quartiles.
The 25th sample percentile is the value
indicating that
25% of the observations takes values smaller than this one.
Similarly, we can define 50th percentile, 75th percentile, and so on.
Note that 50th percentile is the median.
We call 25th percentile the lower quartile
and 75th percentile the upper quartile.
The interquartile range (IQR)
is then defined as the difference
IQR (Upper quartile) (Lower quartile)between them.

The data file may consist of either single column or multiple columns.
Each column is identified with the variable name at the top,
followed by the sample data.
The sample size may vary with the choice of variable
if the column contains blank entries (`NA`'s).