Meta data is data describing other data. In this case the metadata is
what is missing.

We don't have enough information for meaningful comparisons.

That is where I where I am going - and in fact gone.

You are using historical data, without enough context to draw
conclusions about current practice.

So the specific example I gave in fact demonstrates that the useful
information is often well hidden. If we use your approach you have a
statistic that supports the contention that winch launch is 100% more
dangerous than aerotow for this set of data.

Lots of problems -
1 the set is too small (the BGA vs LBA sets are statistically significant)
2 the metric and the generator are not linked. Launch method had nothing
to do with either incident. Poor airfield maintenance and pilot decision
on risk is the cause (both involved a groundloop because someone did not
cut the grass properly and the pilot decided to proceed anyway)
3 the outcome is biased by a "hidden" factor - the actual damage that
resulted in the report of damage to an airframe was traced to
progressive failure of a poor repair after an outlanding accident
decades back when the glider was a competitive two seater in Germany. It
was going to break some time soon. This flight just happened to involve
the trigger stress.

Did the launch method have much to do with the damage, not really. If
the poorly repaired wing failed during spin training, would it mean that
our spin training is dangerous?

So - to be very explicit - where I am going with my comment is that I am
concerned that you may be oversimplifying in an attempt to prove your
opinion. Where an hypothesis would be well enough constructed that is
could be proven.

If you said that the historical accident data for the period you
reviewed showed a difference in the relative safety of operations at
German versus British gliding clubs, that might even be an uncontestable
finding (102). If you compared the trends in accident rates and found
them to be stable over the period you might even be able to conclude
that this is representative of the current situation. (the numbers are
comparable)
If you had qualified the analysis by using the numbers where the
investigators concluded after careful consideration that the launch
method was the causal factor, then you could even conclude that "Winch
launch operations" are more dangerous in one than in the other.

Since you have too little "metadata" and are making conclusion without
all the painful logical and mathematical rigour that makes Business
Intelligence type metrics such a tedious business, I think it is
dangerous and misleading to make the kind of assertions you are making.

Unless you know the actual cause of every number in the set, you can't
make confident assertions.

(Humour alert) There are 10 kinds of people in the world. Those who
understand binary, and those who don't. (10 in binary = 2 in decimal) ;-)

As Bob says, is it possible? Definitely.
Does a simple integer comparison of two numbers prove the assertion? I
think you would have to question that.

Personally, I find winch launching risk to be more tractable. You can
control risk better.

But again - context is important. Winch launching an open class glass
ship with water ballast would probably be less safe than aerotowing the
same combination, all things being equal.

T59D #1771

Not sure where you're going with this, Bruce. Of course there are reasons for the differences and that's a a very important discussion to have but it doesn't affect the difference itself.

The raw accident count for the number of launches done is really metadata (To use a currently popular term.) Metadata is very valuable in seeing the big picture but not so much for analyzing the details for why it looks that way. Hopefully, the metadata will provoke that kind of detailed analysis.


--
Bruce Greeff
T59D #1771