By: Stephanie Pappas, LiveScience Senior Writer
Published: 10/08/2012 11:36 AM EDT on LiveScience

Contrary to the reassuring catchphrase "size doesn't matter," penis size may matter in bed — but only for some women, and for certain types of orgasms.

A new study finds that women who have frequent vaginal orgasms are more likely than other women to say they climax more easily with men with larger penises. Women who tend to prefer penile-vaginal intercourse over other types of sex also say the same, researchers reported online Sept. 24 in The Journal of Sexual Medicine.

"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," study researcher Stuart Brody, a psychologist at the University of the West of Scotland, told LiveScience.

But other researchers were less convinced.

"There's such variability in preference," said Barry Komisaruk, who researches female sexual response at Rutgers University. Women who orgasm through vaginal stimulation may indeed prefer longer penises, Komisaruk told LiveScience, but not everyone prefers to orgasm that way. [10 Odd Facts About the Female Body]

"There are so many different factors," said Komisaruk, who was not involved in Brody's study. "Once it gets to the kind of specifics that they're talking about, I get wary."

The female orgasm

Both penis size and female orgasm are hot-button topics. There is still scientific debate about whether vaginal and clitoral orgasms are different phenomena. Different nerves carry signals from the vagina and from the clitoris, Komisaruk said, and stimulation of each activates different brain regions. 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 told LiveScience.

Other research has found that abdominal exercises induce orgasm in some women, resulting in pleasurable spasms at the gym.

Brody holds a different view, pointing to studies finding that the ability to orgasm with vaginal stimulation alone is correlated with better psychological functioning, better relationship quality and greater sexual satisfaction.

"Earlier research with a large representative sample also found that women who are made aware in their youth that the vagina is a source of women's orgasm are more likely to develop the capacity for vaginal orgasm. Therefore, those who deny these findings (and insist on maintaining the politically correct party line) are not doing women a favor, but might be injuring women's health and sexual potential," Brody wrote in an email to LiveScience.

Does size matter?

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. [Macho Man: 10 Wild Facts About His Body]

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

Finding sexual satisfaction

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.

"To me, all of this is just so goal-oriented, and it's difficult for me to see researchers setting up another goal [vaginal orgasm] for women to experience," Whipple said.

Whipple argued that sexuality is healthier when focused on the pleasure of acts from cuddling to kissing to other sexual sensations rather than the goal of reaching orgasm.

"I recommend for women to learn about themselves, learn about their body, find what they find pleasurable and enjoy that, as long as it's not exploiting another person," she said.

Follow Stephanie Pappas on Twitter @sipappas or LiveScience @livescience. We're also on Facebook & Google+.

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  • 1. Don't Talk Yourself Out Of What You Need

    It's too easy for us women to convince ourselves to settle for less. We're so helpful and accommodating, so eager to please and afraid of rejection that we're quick to give up the things we need, including when it comes to sex. What we need to see is that doing this will leave us chronically frustrated. While it's true that every relationship requires a certain amount of compromise, going without the things that we really need just doesn't work. We'll end up unhappy in the relationship or resentful toward our partner. The bottom line is, we need to know what we can't live without, sexually, and what we just can't live with. We ignore these non-negotiables at the expense of a fulfilling sex life.

  • 2. Share Your Needs And Feelings With Your Partner

    If you can't ask them for what you want in bed, you shouldn't be sleeping with them. Good sex happens when we feel safe and at ease. If we're afraid to ask for something or to tell our partner that we don't like something, sex will never be more than mediocre. This second tip follows from the first one, in that once we identify what we want and don't want, we have to express these things clearly. It's unfair to expect our partner to be a mind-reader and "prove" that they care by somehow knowing what we want without our having to tell them. Healthy sex comes out of healthy communication.

  • 3. Accept Your Body As It Is Now

    We need to be in touch with our bodies; with what feels good, what feels not so good and what feels wrong. We also really need to stop judging ourselves in terms of our weight and our shape. Only a superficial dope would give us a hard time over our imperfections. If someone makes us feel bad about our physical selves, this is more a reflection of his inadequacies than of our own. Our negative self-talk has to stop. The running commentary on how fat we are, how much cellulite or how many wrinkles we have is guaranteed to kill the mood, often before it even starts. Feeling good about our bodies is crucial if we're going to let go and enjoy ourselves. Being physically self-conscious will keep us from experiencing the joyful abandon of great sex.

  • 4. Never Refuse Sex As A Punishment Or Use It As A Reward

    In the bad old days, some women were led to believe that the way to get a man to toe the line is to offer sex for good behavior or withhold it when the man has displeased them. Most of us today recognize this as hateful behaviour and a recipe for disaster. Men don't want to be controlled or punished, especially around sex. They don't want to be made to feel like little boys. When we're hurt or angry at our partner, we need to share our feelings with him in an adult way. We can even say that we're too upset for sex, right now. What we mustn't ever do is make him feel like we're deciding when he gets to have sex, based on whether he's been "good" or "bad." On the other hand, using sex as a reward turns us into sex objects and makes sex into a commodity for our partner to "earn." It's no longer two people being intimate or enjoying each other. Commodifying sex makes it into a business transaction and our bodies then become objects for trade.

  • 5. No Pets In The Room

    We might love Fluffy or Rover, but they don't belong in the bedroom when we're being intimate. Our pets are very territorial and could get jealous or want to play, too. Dogs might bark or even growl. Cats might jump onto the bed and start walking around. We can avoid these disasters by remembering to shut the door and leave our four-legged friends outside.

  • 6. Have A Sense Of Humor

    Sex is about connection and intimacy, but also it's about having fun. It can be mind-blowingly great or occasionally, things can go wrong. Having a good sense of humor about sex will keep things in perspective. Being able to laugh at ourselves and at the comical aspects of sex will take the pressure off the whole experience. We might love and adore our partner, but we don't have to be so serious about making love to them. Humour relieves pressure and is a great way to connect.

  • 7. Enjoy The Give And Take

    The best sex is the kind in which each person is trying to please the other one. The sharing in sex is one of the things that make it great. It can be technically amazing, but when one person gets the impression that the other person really isn't there with them, it can ruin the whole experience. What makes someone a fantastic lover is not their technical ability or their repertoire of moves but their attentiveness and their efforts to make their partner happy. When both people show that they really care about meeting their partner's needs, sex becomes something wonderful.