Data AnalysisNo Comments Satish Harkal

Way to visualize data is by using a box plot or a box and whisker plot. Box plots split the data set into quartiles. The body of the box plot consists of a box, hence the name, which goes from, the first quartile to the third quartile, visually showing you the range of the middle 50% of your data.

Box Plot

Box Plot

Median

This box represents that range. Within the box, a vertical line is drawn at q2, the middle quartile, and this is the median of the data set.

Mean

Sometimes these plots also include a star or something similar to indicate the mean of a data set.

Whiskers

Two horizontal lines called whiskers extend from the top and bottom of the box.

The bottom whisker goes from the bottom of the box to the smallest non-outlier in the data set and represents the first quartile of the data. In other words,it shows the range in which the first 25% of your data fall.

The top whisker goes from the top of the box to the largest non-outlier showing where the last 25% of your data fall.In the data set typically includes one or more outliers, they’re defined as one point times the upper and lower quartile value.They are plotted separately as points on the chart.

BOX

The third quartile is the top part of the box, the second quartile is the bottom part of the box. Thus, box plot show you the range of your data, as well as within each quartile. In addition, they can also review any skewness patterns in your data.

If most of the observations are concentrated on the low end of the scale, the distribution is skewed right.  And if the observations are concentrated on the upper end, the distribution is skewed left.  If the distribution is symmetric, the observations will be evenly split at the median.

Boxplots for Comparing Multiple Populations

Boxplots for Comparing Multiple Populations on Multiple Variables

 

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