Cambridge, Mass. (CBS CONNECTICUT) — A new study asking “Am I Normal?” is the largest body of research analyzing penis size for 15,000 men and uncovers that most men “believe they’re smaller than average” – something experts are calling a perceived distortion of masculinity.

Dr. Abraham Morgentaler, associate clinical professor of urology at Harvard Medical School and founder of Men’s Health Boston, spoke with “CBS This Morning” to discuss his new book, “The Truth About Men and Sex: Intimate Secrets from the Doctor’s Office.”

The book explores male insecurity in the bedroom and refutes many common stereotypes of men being “selfish” in bed. Morgentaler says that “behind closed doors” men are far more concerned with their ability to be a “provider” for their sexual partners.

“We have this idea that men are very simple, but men are actually very interesting, complicated, nuanced and scared” about their penis size and bedroom performance, explained Morgentaler. “We have this idea that men are in this all for themselves when really men have terrific insecurities and concerns because what they really care about is being a provider – a sexual provider for their partner.”

In actuality, says Morgentaler, men have approached him in his urology practice and have deep insecurity about their “sense of masculinity,” which men view as “the key to who they are.” But he adds that many men are hindered by widespread physical problems such as erectile dysfunction and other hurdles to good sexual performance.

Morgentaler says many men’s “sense of masculinity” and ability to be a good partner is dramatically boosted when his partner says “that was great” and other positive reinforcement.

“That’s the best thing a guy can hear,” he says. “And then watch what happens to him – that’s when he can be generous, grand, giving – because he feels intact and whole and great.”

“The number one surprise is that men care deeply and passionately about how they’re doing in relationships,” he adds.

In terms of average penis size, a parallel new study from King’s College London analyzed the question asked by men across the world: “Am I normal?” The men included in the 17 studies were of varying age, weights and sizes. The researchers found a small correlation between height and penis size.

From the study: “The nomograms revealed that the average length of a flaccid penis was 9.16 cm [3.6 inches], the average length of a flaccid stretched penis was 13.24 cm [5.21 inches], and the average length of an erect penis was 13.12 cm [5.165 inches]. The average flaccid circumference was 9.31 cm [3.66 inches], and the average erect circumference was 11.66 cm [4.59 inches]. There was a small correlation between erect length and height.”

If an erect penis is 11 centimeters (4.3 inches), this puts one down in the 10th percentile of study participants, but if one’s erect penis is 15 centimeters (5.9 inches) — that puts a man far up in the 85th percentile.

“We believe these graphs will help doctors reassure the large majority of men that the size of their penis is in the normal range,” lead study author Dr. David Veale explained in a press release. “We will also use the graphs to examine the discrepancy between what a man believes to be their position on the graph and their actual position, or what they think they should be.”

“What’s interesting is, when you look at the curves, you see that most penises actually are fairly similar in size,” Dr. Morgentaler says. “You really have to go to the extremes — the top or bottom 5 or 10 percent — to really see some big differences. And truthfully, in my practice, I would say that’s exactly right. Most men have penises roughly the same size.”

But Morgentaler says men are skeptical of these similarities and have what the study refers to as “small penis anxiety” for many reasons, notably, more access to pornography. Morgentaler also notes that beneficial public discussion on the subject of men’s penis size and sexual performance doesn’t exist as it does for women.

“Men have no voice,” he says. “Women have a voice to talk everywhere, and men don’t.”

Asked about how the effect of Viagra has resonated with men, Morgentaler says one of the biggest results was the opening up of the conversation to a wide public audience.

“Viagra was a game changer, 1998 Viagra came out and boom the world is different,” said Morgentaler. “It’s different, like nobody ever used the word – I don’t even know if I can say it here – the male organ, it was never said on TV before. And all of a sudden you’re hearing prime time ads for it.”

Morgentaler is a leading expert in the field of hormone therapy, especially as it relates to males and testosterone therapy. He is an Associate Clinical Professor of Surgery (Urology) at Harvard Medical School.

— Benjamin Fearnow