Regarding women, Kinsey found in 1953 that nearly 40 percent of the 5,628 women he interviewed experienced at least one nocturnal orgasm (orgasm during sleep), or "wet dream," by the time they were forty-five years old. A smaller study published in the Journal of Sex Research in 1986 found that 85 percent of the women who had experienced nocturnal orgasms had done so by the age of twenty-one, some even before they turned thirteen. In addition, women who have orgasms during sleep usually have them several times a year. Dr. Kinsey and his colleagues defined female nocturnal orgasm as sexual arousal during sleep that awakens one to perceive the experience of orgasm. Girls and women who don't have orgasms in their sleep, or who don't know whether or not they've had them, are perfectly normal. It may be easier for men to identify their wet dreams because of the "ejaculatory evidence." Vaginal secretions could be a sign of sexual arousal without orgasm.