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The Corpulence Index (CI) (also Ponderal Index (PI) or Rohrer's Index) is a measure of corpulence, or of leanness in other variants, of a person[1] calculated as a relationship between mass and height.[2] It was first proposed in 1921 as the "Corpulence measure" by Swiss physician Fritz Rohrer[3][4] and hence is also known as Rohrer's Index.[5] It is similar to the body mass index, but the mass is normalized with the third power of body height rather than the second power.[6] In 2015, Sultan Babar showed that CI does not need to be adjusted for height after adolescence.[4][6]
with in kilograms and in metres, giving a measure with the same dimensions as density. The corpulence index yields valid results even for very short and very tall persons,[7] which is a problem with BMI — for example, an ideal body weight for a person 152.4 cm tall (48 kg) will render BMI of 20.7 and CI of 13.6, while for a person 200 cm tall (99 kg), the BMI will be 24.8, very close to the "overweight" threshold of 25, while CI will be 12.4.[8]
Because of this property, it is most commonly used in pediatrics.[9][10] (For a baby, one can take crown-heel length for the height.[11]) The normal values for infants are about twice as high as for adults, which is the result of their relatively short legs.[citation needed] It does not need to be adjusted for age after adolescence.[6] It has also been shown to have a lower false positive rate in athletes.[12]
The corpulence index is variously defined (the first definition should be preferred due to the use of SI-units kg and m) as follows:
Formula | Units | Values considered normal or typical | |
---|---|---|---|
for a 12-month-old infant | beyond infancy | ||
[9][10] | kg/m3 | 24[9] | 12[6] |
[1][13] | inch * pound -1/3 | 12.49 to 13.92 |
Category | PI (kg/m3[a]) |
---|---|
Underweight | 8-11 |
Normal range | 11-15 |
Overweight | 15-17 |
Obese | >17 |
For infants, units of grams and centimeters are used instead, then the value is multiplied by 100.[17]
Category | PI (child) |
---|---|
Very low | ≤1.12 |
Low | 1.3-1.19 |
Middle | 1.20-1.25 |
Upper middle | 1.26-1.32 |
High | 1.33-1.39 |
Very high | ≥1.40 |
Healthy range | 1.2-1.6 |