In this book, Stuart Sutherland defines irrationality as "any thought process that leads to a conclusion or a decision that is not the best that could have been reached in the light of the evidence, given the time constraints that apply". The introduction out of the way, each chapter then examines factors that lead to irrational thinking, covering topics such as obedience, conformity, overconfidence, inability to interpret statistical data, imagining causes and connections where there are none, ignoring the evidence, sunk cost error, and the all-pervasive availability error.
The discussion about each factor is packed with references to relevant experiments and studies. For example, in the chapter "Mistaken connections in medicine", Sutherland refers to the work of David Eddy, and to a survey which found 95% of doctors unable to correctly interpret the results of breast cancer screening. Eddy found that the inability of doctors to correctly understand conditional probability was leading to many patients being subjected to unnecessary biopsies. In the chapter "The wrong impression", Sutherland gives an example of the halo effect by relating the tale of an award-winning book being anonymously sent to twenty-seven publishers and agents — without the name of the established author attached to the manuscript, the previously award-winning novel was unrecognised and rejected by all twenty-seven who received it.
The examples and studies provide strong backup to Sutherland's argument, very clearly detailing and explaining the common failings of human thinking. The tone of the writing is calm and balanced. Sutherland writes as though he hopes to educate rather than condemn. Chapters end with a moral that offers a few simple pointers to help the reader avoid falling into irrational traps, and the book ends with Sutherland expressing a desire that education be improved to reduce the frequency of foolish errors. He particularly wishes to see professionals properly trained in critical skills such as probability and statistics, so that crucial decisions are taken with the support of rational evaluation of the likely outcomes.
Irrationality is a book well worth reading. It's full of eye-widening information, and it's likely to make the vast majority of people think about the way they approach big decisions.