What is a common reason for percentages exceeding 100% in a chart?

When percentages in a chart exceed 100%, one common reason is that metrics are summed instead of averaged. In many analytical contexts, especially when dealing with multiple categories or dimensions, the percentages are often calculated based on averages of individual group contributions relative to a total. If, instead of averaging these values, the raw sums of the metrics are displayed, it can lead to inflated totals that exceed the expected maximum of 100%.

For instance, if you are looking at multiple segments of users or transactions, calculating the percentage contribution of each segment relative to the whole by summing their values can inadvertently lead to a situation where their combined effect outstrips the total available baseline, resulting in a figure greater than 100%. This approach fails to account for how the segments interact and overlap, especially when aggregating data from multiple sources or views, thus giving a misleading representation of what the proportions actually are.