Parent Center has this handy child Height Predictor
, which asks you for a few simple pieces of information about your child (sex, age, height and weight) and both parents (heights), then calculates an estimate of what your child's height will be at age eighteen.
I, of course, thought it would be fun to play around with their model and see what funky results I could get out of it.
If you have a 3-year boy, who is currently 5-feet tall, and weighs 98 pounds, with a mother who is 6' 1", and a father who is 4' 3", the model comes back with the following:"We ran into a problem while running the calculation. Please make sure you filled in these fields correctly and try again:
Age (Our results show your child would be 9' 4".)"Magnificent. What a family, eh? OK, let's keep the parents the same, but make our boy 3-feet tall adn 40 pounds.
The website replies "Your son will likely be 6 feet, 2 inches tall at age 18. This prediction is a "best guess" but it's still just that -- a guess. Based on the formula we used,* there's a 58 percent chance your son's full-grown height will be within 1 inch (above or below) of this prediction, an 85 percent chance it will be within 2 inches, and an 96 percent chance it will be within 3 inches.
Let's keep the boy the same, and make both parents 6' 2" (what the model predicted last time). I want to see if we keep the same predicted height, but perhaps improve our margin of error.
No! The 58, 85, and 96% figures and the predicted height all remain the same.
What if the parents were both diminuitive (4' 3" as the father in my first test)?
No change!!! Still a predicted 6' 2". So what in the hell do they need the parents' heights for?
The website explains:
"This method relies on where your son falls on the Centers for Disease Control's growth charts, and it assumes that he'll remain in the same percentile until he reaches his adult height. The accuracy of the prediction varies because some children will fall into different percentiles throughout childhood.*Reference:The Multiplier Method for Prediction of Adult Height By Jonathan Paley, Jonathan Talor, Anna Levin, Anil Bhave, Dror Paley, and John E. Herzenberg Journal of Pediatric Orthopaedics, October 2004
Additional answers like in a press release
from back in May of 2005 further detailing the methodology:
"For children under age 4, the improved tool uses the new "Multiplier Method," outlined in the October 2004 issue of The Journal of Pediatric Orthopedics, in which height forecasts are based on average height multipliers calculated from Centers for Disease Control data. For children ages 4 and older, the ParentCenter.com Height Predictor uses the widely accepted Khamis and Roche method that relies on height measurements of each parent for its predictions. ParentCenter.com is the first Web site to integrate the two leading methods into one easy-to-use tool. "
A Ha! So, if I move up to an 8-year old boy who is 3-feet tall and 40 lbs, with parents of 9'3" and 7'3", I should get a tall prediction if the "after 4" model is based solely on the parents.
"Your boy will likely be 5 feet, 10 inches at age 18. Young men often continue to grow a little past 18 until they reach 21, but their height at age 18 is very close to their final adult height. This prediction is a "best guess" but it's still just that -- a guess. Based on the formula we used* there is a 50 percent chance that your boy's full-grown height will be within 0.8 inches (above or below) of this prediction, and a 90 percent chance that it will be within 2.1 inches. The fine print: Parents' heights are a good predictor of a child's adult height, but heredity only accounts for about 70 percent of what goes into deciding how tall someone will be. The other 30 percent comes from environmental factors, like eating habits (poor nutrition can "stunt" a child's growth) and exercise patterns (a competitive gymnast may not grow to her full potential). Sometimes a child will surprise everyone and turn out much taller or shorter than either parent. This calculator can't account for that possibility. It also won't work well for children who 1) are exceptionally tall, 2) are already taller than both their parents, or 3) have a condition that affects their height, such as growth hormone deficiency.
Raising the boy up 1-foot (to 4) and 10 lbs (to 50), holding age and parents' height the same, gives a prediction of 6'10". So the post-4 model must use both child and adult factors, while the model for the under 4 is based solely on the child.
Back to work.