Bill "Laa laa I'm not listening" Zaumen wrote:
>> Oh do attempt to show a little intelligence. Having quoted the base
>> figures, the quoted difference cannot be anything but a percentage
>> change, rather than a percentage points difference.
> When you give X percent for one number and Y percent for another, no
> reader would expect another number expressed as a percent to actually
> be a percentage of a percent.
Interest rates are 5%. The bank raises them to 6% Will your interest
payments increase by 1% or by 20%? But the interest rate has only risen by
1%! Using percentage points differences to de-emphasise the magnitude of
the difference between two figures is a classic technique for lying with
statistics.
In their paper in IP, Crook & Feikh used the percentage points difference
between injury figures to "prove" that helmets are over 60% effective. The
only thng is, they should have used percentage change, not pp. difference -
once that was taken into account what they actually proved was that helmets
are 186% effective, with each helemt not only making its wearer
invulnerable, but also conferring near-invulnerability on a non-wearer.
I note that you have nothing to say about the actual figures, which prove
that you are wrong. I wonder why you are arguing the toss about
mathematical niceties instead of looking at the actual data?
> It is poor and confusing writing on your part (and possibly willfully
> misleading, since casual readers may simply scan the text and jump to
> the wrong conclusion.)
Bill, I have every confidence that you will jump to the wrong conclusion
whatever presentation is used.
In this case they will jump to the right conclusion: the additional aero
drag of a helmet is over twice as great as that of short hair, and somewhat
greater than that of unrestrained long hair.
The casual reader, though, has probably already read the link you posted and
realised that you are talking out of your ****.
>> Of course you prefer the
>> percentage points difference, because it is smaller so suits your
>> disporven assertion
> I prefer it because it is clearer. WHen you see several numbers all
> given as a percentage change from some base value, a reader shouldn't
> have to cross check everything you say to see if you silently changed
> that.
See interest rates example above. Both presentations are defensible in
certain contexts, but when comparing two small percentages, using pp.
difference is more often misleading than not.
>> WHAT teardrop shape? FFS, Bill, get down to that bike shop and
>> actually LOOK at some helmets!
> Like the one I have (a standard helmet). It is teardrop in the usual
> meaning of the word - it sticks out behind the head unlike the older
> completely symmetric helmets.
Brand? Model? Not one helmet in my LBS matches that description. I was
last in a bike shop on Saturday; when were you last in a bike shop?
Note that among the text in the other "evidence" you posted is the bald
statement: "helmet will increase the frontal area of the rider's head and
this will affect the aerodynamics of the rider, thus, the rising of drag.
Therefore, helmet must have a good aerodynamics shape to minimise the effect
of the frontal area. Two track cycling helmets are used to investigate the
performances of drag in different position."
This from the only one of the batch which was actually an academic paper
rather than a discussion of track / TT racing quoting (without attribution)
the Kyle paper as already discussed (that's the one which proves you wrong,
if you remember).
>>>> picture of the Bell Ghisallo, a typical modern helmet. It is not
>>>> "teardrop shaped", it has a pronounced DA at the back.
> I'll describe that as teardrop shaped (unlike a duck, there is a
> smooth taper at the back.)
Ah, so you've never seen one. Thought not. The back of the Ghisallo is
anything but smooth.
>> The evidence yo posted, Bill, which as repeatedly pointed out puts
>> the standard helemt as worsethan the worst-case unhelmeted scenario
>> of unrestrained long hair. I do wish you would go back and read it.
> That's a lie as well - the only helmet shown to be slightly worse than
> long hair was a completely symmetric design - the type where you have
> to look at the straps to figure out which end is which.
You are drowning in your own ********, Bill! Even time trial helmets don't
realise actual drag reductions in real use, as evidence the following quote
from the "evidence" you posted: "[aero] helmets are designed to work
effectively when the rider is facing forward and not to the side. Doing so,
will not only eliminate all benefits gained with the good helmet, but may
also slow you down. And for those who still can't picture what I'm saying,
turning you head while using an aerodynamic helmet is like trying to cut a
piece of butter with the knife laying on its side rather than on its edge."
>>>> Challenged to provide evidene to support your position, you posted
>>>> a page from Damon Rinard which directly contradicts your position.
> It doesn't contradict my position.
Except in the eyes of everybody else who's read it, obviously.
I notice that you haven't responded to this:
http://groups.google.com/[email protected]
>> Anyway, since it is very evident to all concerned that you are wrong,
> More wishful thinking on your part.
You are such a classic zealot it's almost funny. How do you get the Rinard
piece to support your position, I wonder? By not reading past the abstract?
By missing out every third word? Or simply by inverting the sign of all the
drag figures? Who cares, anyway.
> Oh, and due to your bad manners,
> I'll ignore your other post today, since you still haven't grown up.
Translation: "Laa laa I'm not listening".
Guy
--
May contain traces of irony. Contents liable to settle after posting.
http://www.chapmancentral.co.uk
88% of helmet statistics are made up, 65% of them at Washington
University