LOS ANGELES — Yet another study has shown that cardiopulmonary resuscitation, or CPR, by lay people that does not include mouth-to-mouth breathing yields a better chance of survival for people who suffer cardiac arrest outside a hospital.

But even with the technique, which improves the odds of survival by as much as 60 percent, a person's chances of survival are still "dismal," less than about 15 percent, Arizona researchers reported Tuesday. Among the reasons for poor survival are delays in getting resuscitation started, the unwillingness of lay people to use CPR, and lack of knowledge about how to do it.

There are many reasons why mouth-to-mouth may not be advisable for lay people, beyond the fact that many simply do not want to perform it. Among other things, there is a rapid deterioration of blood flow that occurs during even brief disruptions of chest pumping, the long ramp-up time for resumption of normal flow when compressions are begun again after a pause, the significant amount of time necessary to perform breathing and the critical importance of keeping blood flow to the brain going during a heart attack.

In 2007, a Japanese study showed that compression-only CPR could nearly double the survival rate among patients who had a witnessed cardiac arrest. In July, two studies, one in Washington and one in Sweden, found similar results.