Thursday, 26 September 2013

Surveillance math

Suppose there's a low probability chance that any one of us could be pulled aside at Customs for more extensive discussions. It's not happened to me while entering New Zealand anytime in the last, well, decade of living here. But for a couple years, I got the star treatment whenever I arrived in Australia. Why? I think it's because I entered Australia for doughnuts.

I had a couple hours of layover in Sydney on a flight back to Canada. Rather than just twiddle my thumbs in the transit lounge, I cleared Australian customs so I could get some Krispy Kreme on the other side. I doubt that it was the grouchy grouchy Australian customs guy who put me on some watch list, but I rather expect that people who flip into Oz for less than an hour are way more likely to be drug dealers or otherwise dodgy than are other people. One suspicious trip had me on the pull-aside list for a couple years. It got pretty annoying. But it likely made sense from a statistical perspective.

Seeby Woodhouse, a New Zealand tech entrepreneur and, recently, anti-surveillance activist, noted on Twitter last night that he'd been pulled aside for star treatment at NZ customs. I'd reckoned it was just random draw bad luck, but he's since noted that it had never happened on prior trips and that it's also happened to another of the speakers at an anti-surveillance forum.

I don't know the population base rate for being pulled aside by NZ customs. I also expect that the pool of people more likely to speak up at anti-GCSB rallies are also the kind of people who would have greater than average chance of being of interest to Customs officials for other reasons. So even on random-draw pull-asides, a couple of the speakers being pulled aside by Customs after an anti-GCSB rally might not be that improbable even if there hadn't been any rallies.

Martyn Bradbury finds it pretty suspicious, though I suspect he has a pretty low trigger threshold. Let's take his characterisation of the stylised facts though:
One of the most amazing revelations that came out of last nights TICS Bill public meeting in Wellington was Seeby Woodhouse telling the audience that since he spoke out against the Government’s GCSB legislation he was stopped entering America and questioned about his business and shockingly he was pulled aside and questioned by NZ officials when re-entering NZ.
Seeby has been overseas 8 times and has never been questioned, but since speaking out he suddenly gets this type of intimidation. They knew his itinerary, what he had purchased on credit cards and questioned him on what he was doing.
Being pulled aside by the Americans - that seems a reasonably high-probability event for any short duration business trip. Being pulled over on both sides of the trip seems a bit special. Whatever list I was on with the Australians because of my suspicious love for doughnuts didn't get me onto any NZ list, although that was now rather a few years ago. It's plausible that, since then, being pulled up on one side predicts being pulled up on the other.

Not knowing base rates, I can't really run the numbers. If two of the small number of anti-GCSB rally speakers were pulled aside after the rally, and if both hadn't been pulled aside before, and if there's no particular evidence of Customs having otherwise stepped up broad-based enforcement, that does start seeming a bit suspicious.

For now, I'm still calling random-draw. But we're getting close to the threshold where I wouldn't.

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