Robert Shiller says mismatch between Eugene Fama's findings and theories must make him feel like a priest who has discovered God does not exist

It is no secret that two of the three winners of this year's Nobel economics prize disagree – after all, they are economists. But Robert Shiller has taken the tiff with Eugene Fama over the efficiency of markets to a new level.

Highlighting what he sees as a mismatch between Fama's findings and his theories, he suggested his fellow laureate must feel like a Catholic priest who has discovered God does not exist.

While Shiller holds that investors, being human, can be swayed by psychology, Fama contends markets are always efficient, with people incorporating all available information into prices.

To mark their acceptance of the prize last night, the two economists and fellow prizewinner Lars Peter Hansen spoke to Swedish public service television SVT about sharing the Nobel prize for their seemingly opposing theories.

While Fama said it was "great" to share the prize, Shiller was less enthusiastic. "[Fama] is a careful researcher, an inspired researcher," he said, adding: "I don't know if Fama ever states his theory really clearly, if he did it might sound a little odd."

The author of Irrational Exuberance mused that Fama may suffer from "a cognitive dissonance" given, he argued, that his own findings contrast with orthodoxy at his University of Chicago home.

Meanwhile, Fama said there was no way to settle their 21-year debate.

Shiller, whose wife is a psychologist, told SVT (just before 28 minutes into the interview): "I shouldn't try to psychoanalyse Eugene Fama but I know that he is committed … to a libertarian philosophy, teaching at the University of Chicago where Milton Friedman once lived.

"It must affect your thinking somehow that they really believe in markets. I think that maybe he has a cognitive dissonance. His research shows that markets are not efficient. So what do you do if you are living in the University of Chicago? It's like being a Catholic priest and then discovering that God doesn't exist or something, you can't deal with that, you've got to somehow rationalise it."

In his hour-long interview with the official broadcaster for the Nobel prize ceremony, Shiller questioned how much the two really differ and suggests Fama does actually share his "value investing" approach - a consistent policy of buying assets that are low priced and being patient. Where they differ, Shiller says, is on how rational investors are and on how well they can foretell market moves.

"Some people who seem crazy turn out to be smart after all. Apparently that is what Fama thinks. I think they are just crazy," Shiller said, conceding his remarks "may be insulting" to his fellow laureate.

As Shiller puts it, Fama has a "fundamentally different view of the world".

"That's the world we live in, when it comes to economics people have emotions, it's not like chemistry or physics," he said.

In Fama's words, the difference between the two economists is that both see the expected return on a stock as "a price for bearing risk" that can vary through time but that whereas he, Fama, puts that down to "rational variation and the reward for bearing risk" behavioural people like Shiller "say it is market mispricing that eventually gets corrected".

Asked about sharing the prize, Fama has faint praise for Shiller. "I think it's great. Lars has been my friend and colleague for almost 30 years. He does great stuff, it's 180 degrees different than mine. Bob has been around for a long time. He works in the same area. His work is very good and well recognised," he says.