2 + 2 does not equal 3

The human mind is not as rational as we tend to assume from the inside of our own mind. I stumbled across this fascinating example of flawed thinking the other day. Or perhaps it is more fair to label this as a case of flawed estimation than flawed thinking.

A lot of people are concerned with their weight but resent research find that the people most concerned are less skilled at estimating the calorie content of dishes under certain conditions. The different conditions where an unhealthy dish by itself or together with healthy food.
Simple logic would suggest that more food implies more calories but those who estimated the number of calories in the meal rated the options with additional healthy food to have less calories than the unhealthy part of the meal by itself.

More about this research can be read in this paper:
A. Chernev / Journal of Consumer Psychology 21 (2011) 178–183

The people involved in the test where divided into groups and shown different meals and asked to estimate the number of calories. Some rated themselves to be very concerned with their weight and others less concerned. Averaged over the different dishes and groups the people not concerned with their weight estimated the number of calories for the unhealthy dish to be 684 and 658 with the added healthy food item, that is a difference of -26. But the people concerned about their weight estimated the unhealthy option at 711 and the healthy one (more food) at 615, that is a difference of -96.

Even if this research concerns peoples estimation of caloric content of food I would not be surprised if it can be transferred to other areas. How we think should not vary that much with what we are trying to estimate. The explanation that has been put forward for why people make these mistakes is that when you divide something, in this case food, in categorise of good and bad your ability to estimate the combination of them is hampered by to what degree you tend to divide things into good and bad. Many diets are of the kind that they divide foods into categories of good and bad.

It has previously been assumed that concerned people and thus motivated, are less likely to make mistakes. This research has shown that the weight concerned make larger mistakes in estimating caloric content and that is very interesting.