Can someone please help me understand box-and-whisker plots? I get really confused on what each thing is and how to plot it. Thanks.
http://www.google.com/#q=box-and-whisker+plots
Sure! I can definitely help you with understanding box-and-whisker plots.
A box-and-whisker plot is a visual representation of a set of numerical data that provides a summary of the data's distribution. It consists of several components:
1. Minimum value: This is the smallest value in the dataset, usually represented by a small line (often referred to as a whisker) extending downwards from the box.
2. First quartile (Q1): This is the median of the lower half of the dataset. It represents the point below which 25% of the data falls. It is indicated by a line that divides the box into two sections, with the line placed closer to the minimum value.
3. Median (Q2): This is the middle value of the dataset when it is ordered in ascending or descending order. It is represented by a line or small horizontal box inside the main box.
4. Third quartile (Q3): This is the median of the upper half of the dataset. It represents the point below which 75% of the data falls. Like the first quartile, it is indicated by a line dividing the box, but placed closer to the maximum value.
5. Maximum value: This is the largest value in the dataset, also represented by a whisker extending upwards from the box.
To construct a box-and-whisker plot, follow these steps:
1. Order your dataset from smallest to largest.
2. Find the minimum and maximum values. These will be represented as the endpoints of the whiskers.
3. Calculate the median of the dataset, which will form the line or small box inside the main box.
4. Split the dataset into two halves at the median. Find the medians of each half, which will be the first quartile (Q1) and third quartile (Q3) respectively.
5. Draw a line or small box for Q1 to the left of the median line/box, and another line or small box for Q3 to the right of the median line/box.
6. Connect the minimum value to the lower whisker and the maximum value to the upper whisker.
And there you have it! A box-and-whisker plot that visually summarizes the distribution of your dataset.