July 14, 2014

Multiple testing, evidence, and football

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There’s a Twitter account, @FifNdhs, that has five tweets, posted well before today’s game

  • Prove FIFA is corrupt
  • Tomorrow’s scoreline will be Germany win 1-0
  • Germany will win at ET
  • Gotze will score
  • There will be a goal in the second half of ET

What’s the chance of getting these four predictions right, if the game isn’t rigged?

Pretty good, actually. None of these events is improbable on its own, and  Twitter lets you delete tweets and delete accounts. If you set up several accounts, posted a few dozen tweets on each, describing plausible events, and then deleted the unsuccessful ones, you could easily come up with an implausible-sounding remainder.

Twitter can prove you made a prediction, but it can’t prove you didn’t also make a different one, so it’s only good evidence of a prediction if either the predictions were widely retweeted before they happened, or the event described in a single tweet is massively improbable.

If @FifNdhs had predicted a 7-1 victory for Germany over Brazil in the semifinal, that would have been worth paying attention to. Gotze scoring, not so much.

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Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »