Thursday, 30 September 2010

Crowdsourcing the Seismograph

@adzebill took the 11 Twitter guesses of the last aftershock's magnitude, which ran from 3.5 to 6, got an average of 4.37. The actual result? 4.5.

I'd guessed 4.8; I'd not adjusted sufficiently for being up on the 5th floor, where the initial rolling was followed by a sharp jolt and the building groaned. It was definitely bigger than the 4.3 of the other night (experienced at home, ground floor) and smaller than the 5.2 (also experienced ground floor at home).

What were the estimates on this one?

@hamishduff: 3.5 (retweeted)
@ericcrampton: 4.8
@malclocke: 4.4
@rafmanji: 4.0 (retweeted)
@HerrSchnapps: 4.5
@beazer: 4.2
@lightweight: 6+
@90_second_fall: 4.2
@heabe: at least 4.5

So 9 independent estimates, two of them retweeted by the same person so we probably ought not count those two as part of the sample. If we consider only the independent guesses of these nine folks, counting the "at least" folks as giving only a point estimate, then the average for the group is 4.456. The median, which is more robust to the "at least an X" estimates, gives a 4.4. Both are seriously good estimates of the actual magnitude.

I can't find Twitter archive on #eqnz older than 26 September. If anybody knows how to find the older #eqnz tweets, though, there would be a pretty interesting research project in this.
  • Is the median or mean twitter estimate more accurate?
  • Does mean accuracy improve over time with more exposure to quakes?
  • Do individuals who make estimates get more accurate with repeated quakes?
  • How does the variance of estimates move with the magnitude of the quake?
Somebody could have an awful lot of fun with this, if they had access to the full twitter history on the #eqnz channel.

Update: Friday's 5:06 PM shake, 3.7.
The guesses:
"mid-high 3's?" (I'll count as 3.75)
"late 3s, early 4s" (will count as 4.0)
Average: 3.87. A bit high, but not bad.

Update 2: 9 twitter guesses on this one. Average: 4.211. Actual: 4.2. We only actually need the geologists for the initial calibration exercises. Once that's done, we only need the seismographs to make sure we don't stray.

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