Elevated levels of stress hormones were the most reliable predictors of divorce in 90 couples who were followed for 10 years by researchers at The Ohio State University Medical Center. The conclusion surprised the researchers in light of literature suggesting that such conscious actions as negative or aggressive behaviour were the best predictors of divorce. The data showed that women register much higher levels of adrenaline and other stress hormones than men in times of conflict. These higher levels of stress hormones do not go away, even during routine interaction and sleep. Researchers consciously selected couples who were "gloriously happy with each other", lacking risky behaviours or psychiatric diagnoses. They apparently succeeded, with a 19 percent divorce rate through 10 years, about half the national statistics. Consciously, the couples who eventually divorced assessed their happiness much the same as the others when they were newlyweds.