A box plot, also known as a whisker plot, is a standardized way of displaying the distribution of data based on a five-number summary: minimum, first quartile (Q1), median (Q2), third quartile (Q3), and maximum. Below, we will go through the significant parts of a box plot and their meanings.
Significant Parts of a Box Plot
- Minimum: The smallest data point excluding any outliers. This value represents the left end of the whisker on the plot.
- First Quartile (Q1): This is the median of the lower half of the data set (the 25th percentile). It marks the boundary below which 25% of the data fall.
- Median (Q2): This is the middle value of the data set when it is ordered. It divides the data into two equal halves and is represented by a line inside the box.
- Third Quartile (Q3): This is the median of the upper half of the data set (the 75th percentile). It represents the boundary below which 75% of the data fall.
- Maximum: The largest data point excluding any outliers. This value represents the right end of the whisker on the plot.
- Interquartile Range (IQR): The range between Q1 and Q3 (Q3 – Q1). This measures the spread of the middle 50% of the data.
- Outliers: Data points that fall below Q1 – 1.5 * IQR or above Q3 + 1.5 * IQR are typically marked with dots or asterisks on the plot.
In summary, a box plot provides a visual summary of the data through its quartiles and highlights the spread and potential outliers. Understanding these individual components of the box plot is crucial for data analysis, as they help identify characteristics of the data distribution.