It is a new way to measure obesity or if a person is underweight, normal weight, or overweight -- and it doesn't even use your weight in the calculation!
Murray has blogged about it at New measure of obesity – body adiposity index (BAI)
He also made a calculator for it that compares your "results" as far as BMI and this new index, BAI.
This new index uses your height and a measurement around the hips, and it's still somewhat experimental in the fact that it hasn't been thorougly tested in all races.
The formula is
hip (cm) ------------- − 18 [height(m)]1.5
The resulting number should be a close estimate to your body fat percentage.
Just for the record, or if you are curious, I am of normal weight, and supposedly have about 29% body fat according to that calculation. Which, 29% body fat sounds high but it seems to be perfectly normal for females. It makes me think of this age-old saying "Human body is 70% water." That just can't be, not for females anyway. I would be 70% water, 29% fat, and 1% all the other stuff...???
Ok, upon checking I find that indeed, the human body is NOT 70% water. Females average 55% water and males 60% water, but obese people may only be 45% water.