Hat tip to political betting at
for an American article which attempted to provided objective and measurable evidence that people are more likely to make mistakes in their mathematical calculations if the result of those mistakes is to reinforce rather than contradict their strongly held views.
As a statistician I have significant concerns about the way the results of the study are presented, so I would not take the results as gospel. In particular the suggestion that people were 18% more likely to get a calculation wrong if this reinforced their personal particular opinions is rather oversimpllified on the evidence quoted. Nor would I agree that if the study is right - and the jury is well and truly out on that - it would only prove that "politics ruin our ability to think." Any other set of strong opinions, be it about about religion - believer or atheist - or about sport, or tastes in music, might well show the same effect.
What made me sit up an take notice of the article was not the statistics quoted but the graphs.
For a non-political question, (on skin cream) the graphs showing how accurately people with different levels of numerical ability interpreted two sets of data were very similar for Democrat and Republican members of the sample group and irrespective of what conclusion should actually have been drawn from the data.
However, for a political question (on gun control) the four lines on the graph were all different. The great majority of those Democrat voters in the sample of 1,111 respondents who generally had good numeracy skills correctly interpreted the set of data which supported gun control, but about half even of the most numerate Democrats wongly misinterpreted the set of data which did not support gun control.
By contrast the great majority of those Republican voters in the sample who generally had good numeracy skills correctly interpreted the set of data which did not support gun control, but about half even of the most numerate Republicans wongly misinterpreted the set of data which did support gun control.
The moral of this story is that if you are analysing a set of data and the results come out exactly with what fits your prior beliefs, you should try to check your analysis as carefully and objectively as possible to make sure you are not convincing yourself that the new evidence conveniently fits what you were already disposed to believe.