Premier League Predictor: Django & MySQL — Chapter 6, Exercise 2
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TASK
Explain why this chapter resolves the guest-averaging problem by
averaging each guest's own points rather than averaging their raw
predicted scorelines, using a concrete example of two guest scorelines
that cannot be meaningfully averaged directly.

SOLUTION

A football scoreline only means something as a pair of whole numbers —
"the home team scored this many, the away team scored that many."
Averaging two different scorelines field by field doesn't reliably
produce another valid scoreline, because there's no such thing as a
fractional goal actually being scored on a pitch.

Concrete example: one guest predicts 3-0, another predicts 0-2.
Averaging directly gives (3+0)/2 = 1.5 for home and (0+2)/2 = 1 for
away — "1.5-1," which isn't a result any real match could finish with.
This chapter's own worked example (3-0 and 1-0) happens to average to
a coincidentally valid-looking "2-0," but that's just an arithmetic
accident of those particular numbers, not a reliable property of
averaging scorelines in general — the 3-0/0-2 pairing shows the same
operation breaking down completely with only slightly different
inputs.

Points, by contrast, carry no such pairing constraint — they're just
plain integers. Each guest's prediction is scored individually by the
exact same score_prediction() function used for every other source.
In this chapter's worked example, Micah Richards' 3-0 and Jamie
Carragher's 1-0 both correctly identified the real 2-1 as a home win
without the exact score, so each earns 10 points under
POINTS_CORRECT_RESULT. Averaging 10 and 10 gives 10 — a completely
well-defined, meaningful number regardless of what the underlying
scorelines actually were, since two ordinary integers always average
to a third real number with no risk of landing on something impossible.

WHY THIS WORKS AS AN ANSWER
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It explains the structural reason a scoreline can't be meaningfully
averaged (it only means something as a whole-number pair, and
averaging pairs independently doesn't preserve that meaning), supplies
a concrete pair of scorelines (3-0 and 0-2) that visibly breaks when
averaged directly, and explains why points sidestep the problem
entirely since a plain integer average is always well-defined.