How Do Researchers Measure the Onset of Puberty in Boys?

Answers to your questions about the news.
Oct. 22 2012 6:03 PM

A Whole New Ball Game

Why testicular volume has become the gold standard of research into male puberty.

Early teen boys.
A study says that puberty is starting earlier in boys. How can you tell when a boy is going through puberty?

Photo by iStockphoto.

A new study published in Pediatrics indicates that American boys are beginning puberty earlier than previously indicated, with the first signs appearing at age 9.14 for African-American boys, 10.04 for Hispanic boys, and 10.14 for non-Hispanic white boys. What do scientists measure to determine the onset of puberty in boys?

L.V. Anderson L.V. Anderson

L.V. Anderson is a Slate assistant editor. She edits Slate's food and drink sections and writes Brow Beat's recipe column, You're Doing It Wrong. 

Testes size. The earliest sign of puberty in boys is the enlargement of the testicles. Tanner staging, a method of visually assessing the development of secondary sex characteristics (breast development in girls, genital development in boys, and pubic hair growth in both sexes), uses the visual appearance of the testes to determine their length. But the new study used a more precise technique known as orchidometry to determine testicular volume. An orchidometer, also known as Prader beads, is a string of ovoid plastic or wooden beads ranging from 1 milliliter to 25 or 30 milliliters in volume. Prepubertal boys typically have a testicular volume of 1 to 2 milliliters; boys in the early stage of puberty have a testicular volume of 3 to 4 milliliters. (Adult men usually have a testicular volume between 15 and 25 milliliters.) To use an orchidometer, doctors gently pull the testicle to the bottom of a boy’s scrotum and use touch and sight to find the bead that matches it in volume.

Orchidometry is a clear improvement over visual assessments of testis size, since it takes a testicle’s three-dimensional nature into account and isn’t affected by scrotal tension. However, it has the drawback of being more invasive than a visual assessment. More reliable still is an ultrasound, which (unlike orchidometry) can’t be distorted by the thickness of scrotal skin. But since ultrasounds are even more invasive than orchidometers, researchers are unlikely to do any large-scale research on testis size using this method anytime soon. (For clinical rather than research purposes, endocrinologists sometimes prescribe testicular ultrasounds when they suspect developmental abnormalities in boys.)


Only one previous study has documented American boys’ testicular volume using orchidometry , and it was on a smaller scale than the new study, so it’s unclear whether boys are really beginning puberty earlier than they used to—we simply don’t have comparable data from earlier decades.

Though testicle growth is the first sign of puberty in boys, later signs of puberty—including penis growth, thinning of the scrotal skin, changes in scrotal color, and the development of pubic hair—can and have been measured by researchers. Researchers use textbook pictures (either photographs or drawings) to determine which Tanner stage a boy is in. (The Tanner stages range from 1, prepubertal, to 5, fully developed.) Of course, there’s some subjectivity in rating phallic appearance and pubic hair thickness, for instance, which makes measuring these developments across populations difficult. Furthermore, pubic hair growth can sometimes be spurred by hormones released by the adrenal glands instead of those released by the pituitary gland in the course of puberty, which means that pubic hair appearance on its own is not a fully reliable source of information. Although puberty is associated with hormonal changes, measuring hormones in the bloodstream or urine is not considered a useful way of measuring development by most puberty researchers because the correlation between hormonal increases and physical changes is highly variable.

Ideally, puberty researchers would be able to track the physical development of a large number of boys over several years to get a better sense of the average rate of genital growth and timing of specific developments. Unfortunately, this kind of longitudinal study is highly impractical both because of its costs and because of the difficulty of finding boys whose families are willing to enroll them in a multiyear study that involves somewhat invasive measuring techniques. James Tanner did do a longitudinal study of boys to determine the contours of his famous Tanner stages—but that’s because he had a captive sample of 228 institutionalized orphan boys in the 1960s. Performing research on such populations is highly frowned upon today.

Got a question about today’s news? Ask the Explainer.

Explainer thanks Laura Bachrach of Stanford University, Frank M. Biro of Cincinnati Children’s Hospital, and Marcia Herman-Giddens of the University of North Carolina.



Blacks Don’t Have a Corporal Punishment Problem

Americans do. But when blacks exhibit the same behaviors as others, it becomes part of a greater black pathology. 

I Bought the Huge iPhone. I’m Already Thinking of Returning It.

Scotland Is Just the Beginning. Expect More Political Earthquakes in Europe.

Lifetime Didn’t Think the Steubenville Rape Case Was Dramatic Enough

So they added a little self-immolation.

Two Damn Good, Very Different Movies About Soldiers Returning From War

Medical Examiner

The Most Terrifying Thing About Ebola 

The disease threatens humanity by preying on humanity.

Students Aren’t Going to College Football Games as Much Anymore, and Schools Are Getting Worried

The Good Wife Is Cynical, Thrilling, and Grown-Up. It’s Also TV’s Best Drama.

  News & Politics
Sept. 19 2014 9:15 PM Chris Christie, Better Than Ever
Sept. 19 2014 6:35 PM Pabst Blue Ribbon is Being Sold to the Russians, Was So Over Anyway
Inside Higher Ed
Sept. 19 2014 1:34 PM Empty Seats, Fewer Donors? College football isn’t attracting the audience it used to.
  Double X
The XX Factor
Sept. 19 2014 4:58 PM Steubenville Gets the Lifetime Treatment (And a Cheerleader Erupts Into Flames)
  Slate Plus
Slate Picks
Sept. 19 2014 12:00 PM What Happened at Slate This Week? The Slatest editor tells us to read well-informed skepticism, media criticism, and more.
Brow Beat
Sept. 19 2014 4:48 PM You Should Be Listening to Sbtrkt
Future Tense
Sept. 19 2014 6:31 PM The One Big Problem With the Enormous New iPhone
  Health & Science
Medical Examiner
Sept. 19 2014 5:09 PM Did America Get Fat by Drinking Diet Soda?   A high-profile study points the finger at artificial sweeteners.
Sports Nut
Sept. 18 2014 11:42 AM Grandmaster Clash One of the most amazing feats in chess history just happened, and no one noticed.