Box plots, also known as box and whisker diagrams, are a graphical method used to represent data. The box plot is a type of graph used to display data in five-number summaries. These summaries include the minimum, first quartile, median, third quartile, and maximum. Box plots are useful for quickly visualizing the median, range, and spread of a data set in a single graphic view.
Box plots are particularly useful for comparing groups of data. The box plot makes it easy to see how different groups have similar or different medians, ranges, or spreads. In addition, box plots are a useful tool for identifying outliars. Outliars are values that do not belong to the data set due to the nature of this particular box plot they appear more distant from the median value.
The layout of a box plot is simple. It consists of a box, a vertical line within the box and two additional lines above and below the box. The box is drawn between the lower quartile and upper quartile. Quartiles are points which divide a data set into four equal parts. The bottom of the box represents the first quartile and the top of the box represents the third quartile. These two points divide the box in two so the median can be calculated and represented by the vertical line that typically divides the box. The two additional lines, called “whiskers”, extend from the bottom and the top of the box and indicate the extent of the data set.
Box plots have been used for a long period of time, yet many people still find them challenging to understand. However, the information given in a box plot is clearly represented and often gives a better understanding of the data set than other statistical methods. Box plots, therefore, remain a very useful and popular tool for visualizing data.
