When Forecasting Trends, Reading a Bar Chart Versus a Line Graph Biases Our Judgement

hubie writes:

Study suggests that judgmental forecasting of trends in time-series data, such as weekly sales data, is lower when the information is displayed in bar chart format as opposed to a line graph or point graph:

A new study suggests that the format in which graphs are presented may be biasing people into being too optimistic or pessimistic about the trends in data that the graphs display.

Academics from City, University of London and University College London found that when people who were not experts about a set of data made predictions about how a trend in the data would develop over time, they made lower judgements when the trend was presented as a 'bar chart' type graph as compared to when exactly the same data was presented as a line graph or a graph consisting of a set of data points only.

Nevertheless, across many different types of trend participants consistently thought sales would be lower when the data were presented as bar charts than line graphs or point graphs.

The researchers wondered whether the reason was that in bar charts the area inside the bar is usually heavily shaded and hence visually draws attention to itself, lowering participants' estimates as compared to the other types of graph where there is no shading to attract the eye and attention.

However, in a third experiment, they found the same lower forecasts for bars even when the bars were left unshaded.

In a fourth experiment they tested a version of a bar chart where the bars emanated from the top of the graph rather than the bottom. While subtle trends in the data suggest this may reverse the bias, the findings were inconclusive.

Read more of this story at SoylentNews.