On how too much data can make us overconfident in our predictions, rather than boost their accuracy

The problem of more data was investigated by Paul Slovic, Professor of Psychology at the University of Oregon. He ran an experiment with professional horseracing handicap setters in which they were given a list of 88 variables that were useful in predicting a horse’s performance. The participants then had to predict the outcome of the race and their confidence in their prediction. They repeated these tasks with access to different levels of data: either 5, 10, 20, 30 or 40 of the variables.

The results were illuminating. Accuracy was the same regardless of the number of variables used. However, overconfidence grew as more data was harnessed. Experts overestimated the importance of factors that had a limited value. It was only when five data points were used that accuracy and confidence were well calibrated.

Marketers face a similar set of problems. They have access to more data than ever before and many believe that because the information exists they should use it. The Slovic experiment suggests otherwise. We shouldn’t harness data just because we can. Instead, as much time should be spent choosing which data sets to ignore as which to use.

Excerpt from: The Choice Factory: 25 behavioural biases that influence what we buy by Richard Shotton

“Statistics Donโ€™t Stir Us, People Do”

In another experiment, psychologist Paul Slovic asked people for donations. One group was shown a photo of Rokia from Malawi, an emaciated child with pleading eyes. Afterward, people donated an average of $2.83 to the charity (out of $5 they were given to fill out a short survey). The second group was shown statistics about the famine in Malawi, including the fact that more than three million malnourished children were affected, The average donation dropped by 50%. This is illogical: you would think that people’s generosity would grow if they know the extent of the disaster. But we do not function like that. Statistics don’t stir us; people do.

The media have long known that factual reports and bar charts do not entice readers. Hence the guideline: give the story a face.

Excerpt from: The Art of Thinking Clearly by Rolf Dobelli