(Newsroom America) -- Cigarette warning labels can influence a smoker to try to quit even when the smoker is trying to avoid seeing the labels, according to a survey of thousands of adult smokers in four countries published by the American Psychological Association.

Small, text-only warning labels like those on cigarette packs in the United States prompt people to think about health risks of smoking, and people who notice the warnings regularly are more likely to try to quit, the research found.

Larger, more graphic warning labels like those in other countries, such as Australia, were better at getting people's attention and motivating them to attempt quitting, according to the study in the APA journal Health Psychology.

"Warning labels vary widely from country to country but it's clear that once people see the labels, the same psychological and emotional processes are involved in making people consider quitting smoking," said the study's lead author, Hua-Hie Yong, PhD, of the Cancer Council Victoria in Australia.

For smokers who said they paid attention to the labels, simply seeing them was enough to make them think about the health risks of smoking, which made them less likely to smoke a cigarette.

People who didn't think much about the health risks were more likely to say that those risks were exaggerated. They were also more likely to say that they enjoyed smoking too much to give it up, according to the study.

However, smokers who consciously avoided the labels by covering them up or by keeping them out of sight still reported thinking often about the health risks and about quitting.

"This just goes to prove the idea that the more one tries not to think of something, the more one tends to focus on it," said Yong.

Researchers conducted telephone surveys of over 5,000 smokers in the United States, Australia, Canada and the United Kingdom from 2007 to 2009, and then followed up with them one year later.

Smokers answered a series of questions, including how many cigarettes they smoked a day and how often they noticed warning labels on cigarette packages. Researchers also asked them if warning labels made them think about smoking's health risks, if the labels made them think about quitting and if they actively tried to avoid looking at the warnings.

The researchers then asked if they were considering quitting and, at the one-year follow-up, if they had attempted to quit. They collected other demographic information, such as gender, age and education level.

The sample came from the International Tobacco Control Four-Country Survey, a longitudinal study assessing the impact of tobacco control policies around the world.

For this study, 43 percent of participants were men and the number of participants was about equally divided among the four countries. Participants smoked an average of 17 cigarettes a day and 37 percent reported trying to quit at least once at the one-year follow-up.

Because noticing the warnings may be the first step toward getting smokers to think about and attempt to quit, the authors suggested policymakers require that warnings be larger and more graphic on cigarette packages and that they are supplemented with mass media campaigns with similar health warnings.