Question

We see different charts and graphs in our daily lives. How can information and data be presented through different charts and graphs in such a way that the same data is perceived differently based on presentation?

Answer 1

To understand how information and data can be presented through different charts and graphs in such a way that the same data is perceived differently based on presentation, it is best to look at some examples.

Before diving straight to the question let's look at the below example. The data has category-wise sales. If presented in a way that individual bars/sections of pie are not labelled, it becomes extremely difficult to interpret a pie chart. The bar chart is simplistic. You get an idea of the sales by category. For the pie chart, multiple questions arise. Do Footwear and Jewellery have equal sales or one is different from another? How different are makeup, toys and bags?  

Even if the pie chart is labelled (usually in terms of percentage), it is difficult to understand the exact value by which the sections are different - see the below picture as example. If Makeup and Toys differ by 1% (2%-1% =1%), how much is the absolute difference? Is it 1% of 1000 or 10000 or what? This way of presentation makes it extremely difficult to understand pie charts.

Now that we have hopefully developed some understanding of the pie-chart problem let's answer the question with an example. Suppose a store has an offer (Sale!)period going on. We want to look at the average daily sales before the offer period and average daily sales during the offer period by category. The data and charts are given below. These show two direct problems of presenting the same data in different ways.

1. Using percentages instead of absolute values: Notice that during sale, Jewellery sales were 57000 as opposed to pre-sales sales of 50000. Because percentages were used, however, this difference is impossible to tell by just looking at the chart. Both of them have 24% for jewellery - but is this same? No one can tell unless the total sales values are mentioned or the absolute sales values are mentioned rather than percentages.

2. Using pie charts : Aside from the problem discussed above, pie-charts are also inconvenient when there are lot of categories. Imagine 20 categories represented on a pie-chart - it becomes too difficult to even understand the different colours and numbers/percentages!

Basically, if one were to see these charts above, one would clearly understand that Jewellery sales have increased based on the bar chart, but would feel that jewellery sales have remained unchanged by just looking at the pie charts. Thus, the same information in these two charts can be interpreted absolutely differently. Therefore, it is extremely important to be aware of these things to avoid mis-communicating. Try to avoid pie charts, but if it is necessary to use them, make sure to give clear legends, a total number and maybe a small table to help the reader to understand better. You may also go ahead and try scatter plots, stacked bar charts, line charts and understand how sometimes these may mislead the reader in different scenarios.

Hope this helped. Please leave a thumbs up if it did. Thanks!