Using Chart Elements to Ensure Fair and Effective Comparisons across Charts

Here are some basic principles that you should adhere to when designing chart scales
  • Consistent Scale: The scales used in different charts should have the same intervals and proportional sizes. This makes it easier for the viewers to compare the charts without any bias. For example, if you are comparing sales data of two products in two bar charts, make sure the scales for both charts are the same. 
  • Start at Zero: A good practice for designing scales is always starting your y-axis at zero. This prevents the exaggeration of differences between data points and helps viewers accurately represent the data. For example, a bar chart comparing the heights of different buildings should start at a zero baseline to represent the height differences between the buildings accurately. 
  • Use a Logical Increment: Choose an increment for your scale that is easy to understand and consistent across charts. For instance, if you plot a product’s monthly sales over a year, using a monthly increment makes the most sense. On the other hand, if you are comparing sales across years, it would be better to use an annual increment.


Example 1: Comparing Stock Prices 

Suppose you wish to compare the stock prices of two companies, Company A and Company B. You create two line charts to plot the prices over a year. To make this comparison fair and effective: 

  • Use the same y-axis scale for both charts, starting at zero and incrementing logically (e.g., every $10). 
  • Make sure both charts have the same time frame on the x-axis (in this case, one year). 
  • Ensure that the size and overall appearance of both charts are consistent.


Example 2: Analyzing Unemployment Rates 

Imagine you are comparing the unemployment rates of two countries over a five-year period. You create bar charts to plot the data. To make this comparison effective: 

  • Use the same percentage scale on the y-axis for both charts, starting at zero and incrementing by a logical value (e.g., every 1%). 
  • Ensure that the x-axis represents the same time period across both charts (in this case, five years).


Example 3: Comparing Environmental Conditions 

Say you wish to compare air and water pollution levels in a city. You choose to create two pie charts to show the composition of the pollutants. To make this comparison effective: 

  • Ensure the data is represented as percentages or proportions in the pie charts. 
  • Use the same color scheme for the pollutants in both charts to facilitate easy comparison. 
  • If applicable, keep the categories of pollutants consistent across both charts.

Remember, effective chart scale design helps viewers better understand the information and draw more accurate conclusions from your charts.