Double negatives, false positives, Type II errors... Double-sigh (;-) >At that point the FLARM becomes completely useless to everybody ... and that puts us back to exactly where we are now!
> We need that data to evaluate it. The data isn't just one of those things that's nice to have, it's absolutely essential to determine whether FLARM is an inferior offering to what CASA has in mind for us. ...no we don't, 'cause then the statistically pedantic amongst us would observe that ADS-B failure rates for GA/Commercial are not likely to be good indicators of FLARM failure rates in our sport, and we would be no further down the path to continuous improvement than we are now. I'd rather pay a grand now for a commercially-manufactured FLARM which will have marginal but increasingly important benefits as take-up increases, and trust that the commercially astute manufacturer will give me software upgrades when experience allows us to tweak the algorithms for even better reliability. Seems to me that so long as it's a good direction to be going in, we should move in that direction, even if we know there will be further improvements along the way (oops, isn't that just about a definition for continuous improvement?). LOL Brett Kettle -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Mark Newton Sent: Tuesday, 5 July 2005 11:47 AM To: Discussion of issues relating to Soaring in Australia. Subject: Re: [Aus-soaring] FLARM On 05/07/2005, at 11:03 AM, Geoff Kidd wrote: > > Double negatives aside ............ how do you rate the double > positive of a warning that DOES occur when you have no idea that > the other ship is aiming for you HEAD-ON. Sigh. There are four possible modes that a system like this can be working in. * True Negative (Unit is silent, no threats nearby) This is where the typical FLARM installation will spend almost all of its life; the proverbial NULL state. As long as you have some way of testing whether it's still working, this is where you WANT it to spend its entire life. * True Positive (Unit is alerting, threat is actually nearby) This is where the FLARM is correctly alerting you to a potential midair. * False positive (Unit is alerting, no threats are actually nearby). If FLARM units do this more than a handful of times, they will produce an extremely powerful psychological reaction in the pilot, who will say, "The unit is dodgy, it doesn't work, I'm turning it off." At that point the FLARM becomes completely useless to everybody. * False negative (Unit silent, actual threat nearby) This is at least as dangerous as having no FLARM unit at all, possibly more so if the pilot has formed the idea that he can compromise his lookout if the FLARM is going to tell him about midairs anyway. For a FLARM to be 100% reliable, there would need to be 0 incidences of the last two categories. Currently we can probably guess that the false positive category is pretty low, because anecdotal evidence about the usefulness of FLARM seems positive, and if the people telling the anecdotes had been pissed off by errors and turned it off they wouldn't be raving about its virtues. But we presently have no data whatsoever about the false negative category. Would FLARM be worth installing if the possibility of a false negative was greater than the possibility of a true positive? I'd think not. Mike B reckons the ATSB is comfortable with ADS-B having a 25% false negative rate (because it's only expected to prevent 75% of midairs). Do we have any data whatsoever on whether FLARM's false negative rate exceeds that of ADS-B ? We need that data to evaluate it. The data isn't just one of those things that's nice to have, it's absolutely essential to determine whether FLARM is an inferior offering to what CASA has in mind for us. - mark -------------------------------------------------------------------- I tried an internal modem, [EMAIL PROTECTED] but it hurt when I walked. Mark Newton ----- Voice: +61-4-1620-2223 ------------- Fax: +61-8-82231777 ----- _______________________________________________ Aus-soaring mailing list [email protected] To check or change subscription details, visit: http://lists.internode.on.net/mailman/listinfo/aus-soaring _______________________________________________ Aus-soaring mailing list [email protected] To check or change subscription details, visit: http://lists.internode.on.net/mailman/listinfo/aus-soaring
