Moreover, says lead study researcher Jennifer Parker, the new findings delve into the several different types of nightmares that people experience. Among them is the existential nightmare, in which the dreamer loses something or someone they love.
These dreams in particular, she says, were more commonly reported among women. "I think it's a fairly well-established research finding that women report more unpleasant dreams than men," said Parker, a psychologist at the University of the West of England in Bristol. "But I don't think any previous research has picked apart the various differences you have in dreams, which allow different types of nightmares to emerge."
"'Nightmare' should not be used as a blanket term," she said.
Parker studied dream reports from 193 people -- 100 women and 93 men. What she found was that about 19 percent of men reported having had nightmares, while about 30 percent of women reported having them. And she says the type of nightmare reported -- as well as the psychological impact of the bad dreams -- differed between the genders.
"Existential nightmares appear to be far more disturbing for women," she said. "They are much more upsetting to women than the fearful nightmare, and many women wake crying from them."
Some sleep researchers, however, cautioned against reading too much into the results of the relatively small study.
"It is important not to over-interpret the finding of more recalled nightmares by assuming this means there are more of them actually happening," said Dr. David Rapoport, associate professor of medicine and director of the Sleep Program at the New York University School of Medicine. "We only remember a small number of the dreams -- and nightmares -- that are found when we are queried after an arousal."
Rosalind Cartwright, dream research and chairman of psychology at Rush University Medical Center, agrees. "This was a self-report survey. We know that ... nightmare frequency, when you collect the data in that way, is very different from when you log it every day."
But she adds that the new research once again demonstrates how women tend to have better recall when it comes to dreams, including disturbing ones. And she says this and other studies shed light on how women might "process" emotional occurrences in their day-to-day lives.
"It seems to be related to women being a little more inwardly oriented, paying more attention to their feelings, and being more self-critical," she said, adding that women would also be "more likely to carry [these feelings] into bed" and subsequently dream about them.
"We know that any experience from your waking hours that has an emotional tag is likely to be carried forward into sleep," Cartwright said.
Who You Are Is How You Dream
The study is not the first to home in on particular demographic variables to try and separate those who are more likely to have nightmares from those who have a better chance of dreaming peacefully.
Cartwright says many of these variables are easy to understand. "They are the ones you might imagine, anything that makes for distress and disadvantage," she said. "These include low income, unemployment and other factors."
But past research reveals some surprises. A July 2001 study by researchers at the University of California, Santa Cruz, suggested that Republicans are nearly three times as likely as Democrats to experience nightmares when they dream.
"Half of the dreams of Republicans in my study were classified as nightmares, compared to only about 18 percent of the dreams of Democrats," said lead study author Kelly Bulkeley in a university-issued press release. "My speculation is that people on the right are very attuned to the dangers in the world, and they're seeking ways to defend themselves against those threats."
Still, many researchers are hesitant to read too deeply into the frequency and recollection of nightmares and less severe bad dreams. New York University's Rapoport notes that, in particular, those who study dreams should be particularly careful not to impose certain stereotypes upon nightmare frequency. And he says that the conclusions of this most recent study may cross that line.
"The finding of the study is clear -- women have more recalled nightmares," he said. "The conclusions are less so."
He says that while women may be reporting more nightmares, there needs to be proof that women are actually having more nightmares before researchers come to a conclusion -- especially, he notes, "one based on soft issues like women being 'more emotional' or 'more involved with relationships.'"
How Our Dreams May Help Us
Regardless of how the research is interpreted, however, Cartwright says dreams and nightmares can offer important clues to help patients in the clinical setting.
"There's a mood-regulating function of dreaming," she said. "So what dreaming does throughout the night is defusing the negative aspects of our experiences. That basic aspect of dreaming having that function has now been supported by a lot of research."
Cartwright has developed a treatment program for nightmares based on this principle, and she says that it has shown particular success in women who have been raped or assaulted. The treatment, she says, involves empowering a woman by encouraging her to take her nightmare and design a better ending.
One of her patients, a woman who had been raped as a teenager, found that her experiences were having a negative impact on her ability to be intimate with her new husband. Her trauma had also led to nightmares so intense, Cartwright says, that "she would soak her sheets at night perspiring."
In one of the recurring nightmares, the woman said she was lying flat on her back in an elevator with no walls, climbing higher and higher above the city skyline.
"I said to her, 'OK, how would you change the ending to make it better?' She said, 'Well, I could stand up for myself,' which is a lovely metaphor."
By changing her dreams, Cartwright says, the patient was able to cope with the real trauma she carried into her relationship.
Parker says her research will hopefully extend dream and nightmare analysis further into the clinical setting. "I think dreams are useful for determining what we might need to change in our lives; they can give us that alarm call," she said.
"If you look at your dreams as being consistent with your waking life," she said, "then there are implications in terms of what these dreams can tell us."