--- In morelife@yahoogroups.com, François ROSE <fr.rose@...> wrote:
>
> Hi Paul and Kitty
> I hope you are well
> Here is a report of a recent exchange between Olafur, you (Paul) and
> me about the right use of rate in vernacular englsih
>
> Here is the caption (I'm not sure about the term) of this dialog
> >>>>>> Me (to Olafur)
> >>>>> Olafur (to me)
> >>>> Me (to Olafur)
> >>> Me (to Paul)
> >> Paul (to me)
> >Olafur (to Paul)
>
> I also wrote the initial of the author at the beginning of the line
> in order to be clearer
>
> [Thanks for doing that. With a three way inline discussion the
> "level indicators" are not as easy to follow as with a dialog. --Paul]
>
> [As an explanation, this email correspondence occurred on the side
> from a thread discussion on calorie restriction between Olafur and
> Francois at sci.life-extension a few days ago - http://tinyurl.com/5zao3x
**Kitty]

It is a long thread with several other participants, including me at
the start.


> F>>> Olafur and I are arguing about the right use of rate. Would
> F>>> it bother you to enlighten us ? (I pasted below the recent
> F>>> exchange with Olafur)
>
> F>>>>>> Hi Olafur,
> F>>>>>>
> F>>>>>> I'm making my answer to your questions about my fat rate
> F>>>>>> (which is much higher than you, you'll see)
>
> O>>>>> Actually it's fat percentage not fat rate. As far as I know
> O>>>>> the word "rate" is only used to describe the speed of
> O>>>>> something like heart rate, the speed at which
> O>>>>> the heart beats.
>
> F>>> About rate, I think its use here is correct AFAIK but maybe
> F>>> I'm wrong.
>
> P>> In vernacular English, rate is always be used to describe the
> P>> measured change in some parameter per unit of time.
>
> O> Yes I was almost 100% sure the word rate could only be used when
> O> speaking about *change* in some parameter. Therefore I was certain
> O> that his use of the phrase fat rate was incorrect
> O> precisely because I had asked him about his fat
> O> percentage (which is the amount of fat he is carrying as a
> O> percentage of his bodyweight)not how fast his body fat
> O> was *changing* in either direction.
> O> Maybe the French equivalent word for "rate" can be correctly
> O> used along with the French equivalent
> O> word for "fat" to mean fat percentage in French? I don't know,
> O> but I do know that similar things confuse me sometimes when I
> O> think about the equivalent Icelandic
> O> words for some English words.

Actually my use of the word "always" above was incorrect since upon
doing some dictionary research, I realized that I had not remembered
that "rate" is also often used in a way not relating to time (as in
hotel room rate, tax rate, interest rate, discount rate, wage rate -
which is not necessarily per unit of time, the price charged an
advertiser per unit of publication space or of radio or television
time, etc). So in that respect it comes very close to ratio,
percentage and, yes, even "fat rate". Still, I have never heard "rate"
used with respect to fat percentage and although I think most people
would understand, they might suspect that the user was not a native
English speaker. Olafur still uses a few words in ways that are
"strange" for a native English speaker. OTOH, there is also great
variation among native English speakers. I too use words in somewhat
different ways than many native english speaking people, but I do so
mostly intentionally for a purpose and do know what others mean when
they use them differently.


> That's the case: in french "taux" can be translated in english
> either by ratio or by rate

Aha! And which translation is correct english usage will depend on the
context and experience with english. This is a good example of why
machine translation is so difficult.


> P>> However, that notion is
> P>> generalized in calculus to signify the instantaneous change of
> P>> any variable with respect to another with respect to which it has
> P>> a dependency relationship (technically merely called
> P>> a relation).
> P>> Speed is merely one special kind of rate, the change
> P>> of distance with time - even though speed is often
> P>> incorrectly used for other types of rate (eg.
> P>> reaction rate is sometimes, incorrectly, called reaction
> P>> speed). Rates should never be expressed as percentages, since a
> P>> percentage is merely a ratio of two measurements in the same
> P>> units, of quantities with no necessary dependency except that
> P>> one measurement (the denominator) is a
> P>> part or super-part of the other measurement (the numerator).
>
> Until this, I think I fully understand your reasoning, Paul:
> If I say, my fat rate is 16.4 %: it's a wrong use
> If I say, my fat ratio is 16.4%: correct use

Correct.


> P>> It would be
> P>> correct to to apply the term rate to body fat if one used it to
> P>> express the change over time of one's percentage or amount of
> P>> body fat.
>
> O> Thanks for the accurate explanation.
>
>
> Here I'm a bit puzzled; do you mean that I could say:
> my fat ratio was 16.9% a year ago; it's now 16.4% so my body
> fat rate is equal to (16.4-16.9)/16.9 =-0.0296 which means a
> decrease of 2.96% of my fat ratio
> If I understand your point, it is a correct use but of course nobody
> states things like this regarding fat ratio.

Yes, it is not generally stated that way. However it would be
perfectly correct and fully understandable to state that your body fat
percentage was decreasing at a rate of 2.96% per year. But note that
this is very different than saying that your body fat percentage
decreased by 2.96% (since it only decreased by 0.5%) and also slightly
different from the rate per year of decrease in your body fat amount
(because your total weight also changed), as you found out in your
calculation below.


> (Moreover there is a reasoning error since 16.9% of 62.6 kg= 10.579
> kg of body fat and 16.4% of 62 kg = 10.168 kg of body fat so my body
> fat rate is (10.168-10.579)/10.579=-0.0389=-3,89%

The above would more correctly be stated as:

"so my body fat rate of decrease per last year was .... = 3.89%".


> though my body fat ratio has decreased of 2.96%

I do not understand why you think/write that there appears to be some
"reasoning error". Perhaps you have fallen into the common fallacy of
misapplication of logic to percentages. When I first read the above I
too thought that the second calculation would be smaller number than
the first. I suggest that working through the logic of these sorts of
calculations (which seem to be intuitively incorrect) would be a good
exercise for your math students.


> (it is normal that the body fat rate
> is lower than the decreasing of the body fat ratio since the body
> weight has also decreased of 600 grams))

What your logic here is missing is that the decrease in body weight
makes the new fat weight larger than it would have been if only the
fat weight had decreased. Since that part is subtracted, this results
is a larger numerator and an increased ratio (in absolute terms).


> Maybe more interestingly than what I've wrote just above, these
> calculations show that when I lose 600 grams of body weight, I lose
> 411 grams of body fat (and the remaining 189 grams must be water and
> muscle)

Yes, one always loses some muscle with the fat (and some
bone/cartilage also). That is why exercise is necessary to keep both
of these losses from being unhealthily large.

--Paul