Colleagues,
BMI has is failures, but it has demonstrated utility. BMI predicts multiple
outcome measures including cardiovascular disease and mortality. Don't
through out a useful metric because it is not the perfect metric.
As to why BMI is computed as weight/height^2, it can be shown that dividing
height by the square of weight decreases the correlation between weight and
height. The optimum exponent (i.e. the power that most effectively minimizes the
correlation between weight and height) is not the same in men and women and it
differs by race. In general an exponent of 2.0 is best for men; for women an
exponent of 2.2 is a bit better than 2.0.
In any event, don't let the perfect get in the way of the good.
John
John David Sorkin M.D., Ph.D.
Professor of Medicine
Chief, Biostatistics and Informatics
University of Maryland School of Medicine Division of Gerontology and Geriatric
Medicine
Baltimore VA Medical Center
10 North Greene Street
GRECC (BT/18/GR)
Baltimore, MD 21201-1524
(Phone) 410-605-7119
(Fax) 410-605-7913 (Please call phone number above prior to faxing)
________________________________________
From: R-help <r-help-bounces at r-project.org> on behalf of Jim Lemon
<drjimlemon at gmail.com>
Sent: Monday, March 1, 2021 4:23 PM
To: Richard O'Keefe; r-help mailing list
Subject: Re: [R] Image processing in R for BMI calculation
I must agree with the criticism of BMI as a diagnostic index. It is
easy to tell if a person is - ahem - wide and not very high with a
single glance. These elementary parameters can easily be deduced from
an image of said person. However, it does not convey that essential
ratio of muscle to - ahem - adipose tissue that is the stated reason
for its prominence. I suggest an older, but more valid, index that was
used in the identification of witches. Simply tie the person's hands
behind their back and throw him or her into the deep end of the pool.
Time to drowning is the response variable and I am certain that those
now chastised for their adipose tissue will vastly prefer it.
Jim
On Mon, Mar 1, 2021 at 10:24 PM Richard O'Keefe <raoknz at gmail.com>
wrote:>
> "Body Mass Index" is a rather bizarre thing:
> body.mass.in.kg / height.in.m^2
> I have never been able to find any biological
> or physical meaning for this. Yet clinicians
> are solemnly advised to measure the weight to
> the nearest 0.1kg and the height to the
> nearest 0.1cm.
>
> How do you propose to determine the weight from
> a single image? Even an R package cannot perform magic.
>
>
> On Mon, 1 Mar 2021 at 05:39, Paul Bernal <paulbernal07 at gmail.com>
wrote:
>
> > Hello everyone,
> >
> > Does anyone know about any package for image processing, for example,
to
> > calculate body mass index pased on a picture, silouette or image.
> >
> > Any guidance will be greatly appreciated.
> >
> > Best regards,
> >
> > Paul
> >
> > [[alternative HTML version deleted]]
> >
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