# Obesity and body roundness indicator

**URL:** <https://boards.straightdope.com/t/obesity-and-body-roundness-indicator/1007297>\
**Category:** Miscellaneous and Personal Stuff I Must Share\
**Created:** [September 15, 2024, 1:10pm UTC](https://boards.straightdope.com/t/obesity-and-body-roundness-indicator/1007297 "2024-09-15T13:10:43Z")\
**Posts on this page:** 5\
**Page:** 2

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**Author:** ![echoreply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/echoreply/32/3641_2.png) [@echoreply](https://boards.straightdope.com/u/echoreply)\
**Post date:** [September 16, 2024, 8:04pm UTC](https://boards.straightdope.com/t/obesity-and-body-roundness-indicator/1007297/21 "2024-09-16T20:04:47Z")

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> [@Hari\_Seldon](#):
>
> What is \piπ\pi doing there anyway, except to make it spuriously “scientific” looking

It ain’t “round” if it’s missing \pi. BMI is “squareness”, with the \rm{height}^2 term, and BRI has to distinguish itself from that.

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**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\
**Post date:** [September 16, 2024, 8:05pm UTC](https://boards.straightdope.com/t/obesity-and-body-roundness-indicator/1007297/22 "2024-09-16T20:05:16Z")

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> [@Hari\_Seldon](#):
>
> What is \piπ\pi doing there anyway, except to make it spuriously “scientific” looking.

I think they’re modeling the body as an ellipsoid, so the 2\pi converts the waistline into a radius, and the half-height is the, uh, semi-major axis. Then they added a bunch of other fudge factors.

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**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\
**Post date:** [September 16, 2024, 8:06pm UTC](https://boards.straightdope.com/t/obesity-and-body-roundness-indicator/1007297/23 "2024-09-16T20:06:17Z")

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> [@echoreply](#):
>
> It ain’t “round” if it’s missing \piπ\pi. BMI is “squareness”, with the \rm{height}^2height2\rm{height}^2 term, and BRI has to distinguish itself from that.

But that can’t possibly add to its predictive value since it’s just a fixed scaling factor.

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**Author:** ![echoreply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/echoreply/32/3641_2.png) [@echoreply](https://boards.straightdope.com/u/echoreply)\
**Post date:** [September 16, 2024, 8:26pm UTC](https://boards.straightdope.com/t/obesity-and-body-roundness-indicator/1007297/24 "2024-09-16T20:26:36Z")

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> [@Dr.Strangelove](#):
>
> that can’t possibly add to its predictive value since it’s just a fixed scaling factor

Explain that to my wife when I leave \pi out of calculating pizza value!

As a researcher, I view changing the measure as a difficult hurdle. The new measure has to be _much_ better. The old measure (BMI) already exists in every relevant dataset going back centuries. This is a huge advantage. Lots of literature exists related to BMI, which can give researchers a good sense of how it behaves with respect to other things you’re more interested in.

The main advantage of BRI, is that because it is relatively new, you can publish a bunch of papers redoing old BMI analyses with BRI instead. Unless BRI is capturing an important\[1\] amount of variance over BMI, it probably won’t gain much traction.

There’s also the triggering thing. People react poorly to BMI, so maybe BRI will make doctor’s jobs easier. Over half the people in the US would greatly benefit from exercising more and dropping 15-30 pounds, regardless of how it is quantified.

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1. and _important_ is different than _significant_

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<div class="post-metadata">

**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\
**Post date:** [September 16, 2024, 8:36pm UTC](https://boards.straightdope.com/t/obesity-and-body-roundness-indicator/1007297/25 "2024-09-16T20:36:21Z")

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> [@echoreply](#):
>
> The new measure has to be _much_ better.

The thing is, it’s not actually new. As **Hari\_Seldon** noted, this is just a dressed-up waist-to-height ratio. It can’t be more predictive than that. And waist-to-height has already been analyzed a fair amount.

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