State of GA safety (2005 Nall Report)

by Jose Mar 9, 2006 at 08:06 PM

The key assumption in one case is that the numbers are consistent, in
the other that they are accurate.


Systematic and random error are two totally different beasts.

Jose



I do understand what you are saying: I learned the important distinction
between "precision" and "accuracy" many years ago as an undergrad science
student.

The BTS conclusion depends upon the accuracy of the "hours flown"
estimate. The Nall Study's validity depends more upon the precision
(using a method that can repeatedly reproduce the same result within a
small margin of error) of the estimating technique than on its absolute
accuracy. Thus even if the hours flown estimate is "systematically"
misestimated (i.e. is inaccurate) it would not invalidate the conclusions
of the trend analysis conclusion. Yes?

But this is really splitting hairs. The BTS study showed subsidies so
large that even if there was huge sampling error or other statistical
mis-steps that resulted in a vast underestimation of hours flown (and
therefore exaggerated GA subsides), the conclusion is still valid: that
GA is very heavily subsidized relative to other modes of transportation.


Just looking at the raw revenue number from the funding sources also makes
this quite obvious. (I'd repost the BTS data, but I've been yelled at
already for reposting the stuff....)

Thus even if the hours flown estimate is "systematically"
misestimated (i.e. is inaccurate) it would not invalidate the conclusions
of the trend analysis conclusion. Yes?

Yes.

The BTS study showed subsidies so
large that...

I haven't read the study so I can't really comment on it intelligently.
But like the difference between precision and accuracy, there is a
difference between pro-rated costs and marginal costs which needs to be
taken into account. One must also consider who benefits - it's not just
the immediate users.

And even if xxx were subsidized, that's not necessarily a bad thing.

Jose
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.

wrote in message
ups.com...
I read on AvWeb today the '05 Nall Report is out, and apparently 2004
was a historic low for aviation accidents. This led me to question what
next year's report will look like after considering the spate of GA
accidents that we've all read about in the last year or so. Maybe it's
just a question of perception? Or, are pilots just getting too
complacent when they strap into their aircraft?


You mean "considering the spate of people posting every GA accident they
come across"...

I don't see how the morbid fascination of some individuals here could have
any effect on the actual number of accidents.

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
Spell checking is left as an excercise for the reader.

You mean "considering the spate of people posting every GA accident they
come across"...

Well, as I am a frequent visitor to this forum I suppose that could
have influenced my perception.

I don't see how the morbid fascination of some individuals here could have
any effect on the actual number of accidents.

It doesn't.

C'mon King, what hiding place?

Uh, your cave?

I don't like to engage in ****ing matches just for the hell of it..

Really? This can't be the same Skylune we all know and love here on
RAP...

On Chicago: surely you jest!

I'm not jesting. And don't call me shirley. (you asked for that)

For those who want to do their own statistical analysis, this is an
interesting site:

http://www.ntsb.gov/ntsb/query.asp


Limit the date range to Jan. 1 - Dec. 31, 2005 and plug in your favorite
manufacturer in the Make/Model box.
You'd be amazed.




wrote in message
ups.com...
I read on AvWeb today the '05 Nall Report is out, and apparently 2004
was a historic low for aviation accidents. This led me to question what
next year's report will look like after considering the spate of GA
accidents that we've all read about in the last year or so. Maybe it's
just a question of perception? Or, are pilots just getting too
complacent when they strap into their aircraft?

On 2006-03-09, wrote:
I guess that's the real *big picture* view then. I'm not immune to
altered perceptions when it seemed for a while there were 1 or 2 GA
accidents a week.

One or two a week? There are almost always at least a dozen GA accidents
a week. If you go to the 'browse' view on the NTSB website, you'll see
there are far more days with multiple GA accidents than there are days
with no accidents at all. I went to September 2005 (picked at random, no
reason) and there were NO days in September 2005 where there were not at
least 2 GA accidents. Most days had about 5 or 6 GA accidents. There
were 31 fatal GA accidents in September 2005 - one more than September
has days.

You're probably only percieving a cluster because they have been talked
about more, but really - the accidents that have been talked about here
recently are not out of the ordinary (sadly).

--
Dylan Smith, Port St Mary, Isle of Man
Flying: http://www.dylansmith.net
Oolite-Linux: an Elite tribute: http://oolite-linux.berlios.de
Frontier Elite Universe: http://www.alioth.net

Clustering can reduce the rate for one year and elevate it for another
year. However, the report shows that accident rates have been declining
for the past 10 years, which is a significant point.


Jose wrote:
I read on AvWeb today the '05 Nall Report is out, and apparently 2004
was a historic low for aviation accidents. This led me to question what
next year's report will look like after considering the spate of GA
accidents that we've all read about in the last year or so. Maybe it's
just a question of perception? Or, are pilots just getting too
complacent when they strap into their aircraft?

Or maybe it's just a statistical artifact. Shift a few accidents from
December to January, and shift a few others from next January to this
December, and you have a banner year for airplane crashes caused simply
by the artificial boundaries of the sample set.

Sometimes random events cluster for no reason. In fact, it is highly
unlikely that they would =not= cluster.

Jose
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.

Dylan wrote:
One or two a week? There are almost always at least a dozen GA accidents
a week.

I realize this, I guess I was just referring to the accidents that got
local or national attention.

You're probably only percieving a cluster because they have been talked
about more, but really - the accidents that have been talked about here

recently are not out of the ordinary (sadly).

Yeah, I mentioned it probably being a question of my own perception
because of the ongoing discussion on this forum of recent accidents.
And yes, it is sad.

Andrew wrote:
Clustering can reduce the rate for one year and elevate it for another
year.

Right, Jose mentioned this in his reply to my OP

However, the report shows that accident rates have been declining
for the past 10 years, which is a significant point

That IS good news. I'm curious to see how/if '05 follows to the overall
trend.