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There is a debate raging in the hallowed halls of academia. Well, OK, so ‘raging’ may be an exaggeration, but there is a definitely a debate, and it’s a biggie.

For years now, there has been an idea about will-power called ‘the theory of ego depletion’. Strong evidence has been presented in favor of it, and it has been pretty much accepted as fact. Indeed, we presented it as a fact in the book. Here’s what we wrote:

The bad news about willpower is that we do not have an endless supply of it. To demonstrate this, the psychologist Mark Muraven asked one half of a group of people to relax, and the other half to do something rather strange. He asked them to not think of a white bear. That may sound simple enough, but you try it. Whatever you do, do not think of a white bear. For most people, once you’ve been told not to think of something, it is almost impossible not to. It takes a lot of self-control.

After five minutes of this, Muraven told his participants that they would next be having a driving test, but that they could have a glass of beer or two beforehand if they wanted. The results were surprising. The people who had been using their self-control trying not to think of a bear drank more beer than those who had just been relaxing. They simply had less self-control left. Other studies that have asked people to wait before eating some cake have found similar results. Individuals asked to expend some self-control by waiting five minutes before eating some cake, subsequently ate more than people told they could eat the cake immediately. So using self-control on one task reduces the amount we are able to use on a subsequent task. It seems we only have so much self-control to go around.

The really big piece of evidence support this idea that will-power is in limited supply was a 2010 meta-analysis – a type of study that looks at the results of other pieces of research, and in this particular case over 200 other pieces of research. Convincing stuff.

Now, however, a new study has questioned how good that 2010 meta-analysis really was. It suggests that some of the pieces of research included in the original meta-analysis may have been flawed and to correct this, it gathered a new set of studies, using stricter criteria for inclusion. It also made sure to not just look at published studies, but to also go hunting for unpublished studies. The reason this is significant is that sometimes when psychologists conduct experiments and don’t get a positive result or one that supports a prevailing theory the paper doesn’t get published. So by including unpublished studies, the new meta-analysis was more likely to include research that did not support the prevailing ‘ego depletion’ theory. And lo and behold, that is exactly what they found – that there was not enough evidence to support the idea that will-power is a limited resource. Instead, they even found some evidence to support the opposite idea (what is sometimes called ‘learned industriousness’) – that will-power can improve through successive challenges.

So where does this leave us? In the middle of a bun fight, to be frank. If the ego depletion theory is wrong and if learned industriousness is correct then it would have some interesting implications for how we can prepare ourselves for challenges. But for the moment the evidence is not strong enough to be sure. Supporters of the ego depletion theory will almost certainly counter and it is likely to be a few years yet before this debate is settled.

In the meantime, we need to remember that the evidence that will-power can be improved with practice has not been questioned. So regardless of whether continued effort reduces our self-control in the moment, we all have the power and opportunity to improve our levels of will-power over time.