Women who tend to prefer penile-vaginal intercourse over other types of sex also say the same, it said.

"Male anxiety about penis size may not reflect internalized, culturally arbitrary masculine stereotypes, but an accurate appreciation that size matters to many women — just as men feel legitimate anxiety when they enter the mating market about their intelligence, personality traits, sense of humor, social status, height, wealth, and other traits known to be favored by women across cultures," the Huffington Post quoted study researcher Stuart Brody, a psychologist at the University of the West of Scotland, as telling LiveScience.

But other researchers were less convinced.

Women who orgasm through vaginal stimulation may indeed prefer longer penises, but not everyone prefers to orgasm that way, said Barry Komisaruk, who researches female sexual response at Rutgers University, told LiveScience.

But some researchers argue that vaginal stimulation is simply activating a different, internal, section of the clitoris. Women report different sensations from vaginal and clitoral orgasms, Komisaruk said, but which one women prefer largely comes down to personal preference.

In some cases, female orgasm is even more complex. For example, Beverly Whipple, professor emerita at Rutgers University and one of the discoverers of the G spot, a sensitive area felt through the front wall of the vagina, has found that women with complete spinal cord injuries can sometimes experience orgasm, even though the nerves that carry sensation up the spinal cord from the pelvis have been severed.

It's likely that the sensory vagus nerve, which runs in the abdomen but bypasses the spinal cord, is recruited to carry signals to the brain in these cases, Whipple toldLiveScience.

In the new study, Brody and his colleagues asked 323 women, mostly Scottish university students, to recall past sexual encounters. They were asked about their recent sexual behaviors as well as how important penile-vaginal intercourse and other sex acts were to them. They were also asked whether penis length influenced their ability to orgasm with vaginal stimulation.

Defining "average" as the length of a 20-pound banknote or U.S. dollar bill, which are 5.8 inches (14.9 cm) and 6.1 inches (15.5 cm) long, respectively, the researchers asked women if they were more likely to orgasm vaginally with a longer-than-average or shorter-than-average penis.

They found that 160 of the women experienced vaginal-only orgasms and had enough sexual partners to compare size experiences. Of these, 33.8 per cent preferred longer-than-average penises, 60 per cent said size made no difference and 6.3 per cent said longer was less pleasurable than shorter.

Supporting the hypothesis that size matters, Brody and his colleagues found the women who reported the highest number of vaginal orgasms in the past month were most likely to say that longer was better.

"This might be due at least in part to greater ability of a longer penis to stimulate the entire length of the vagina, and the cervix," Brody said.

The data supports Brody's claim, Whipple said, but the sample is limited to Scottish university students and should be replicated with a broader group. Nevertheless, she warned against worrying about the findings in bed.

The researchers recently reported online in The Journal of Sexual Medicine.