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.'"
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."