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StackOverflow2013
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PO
 

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    <p>For each post, generate bounds on how helpful you expect it to be. I prefer to use the Agresti-Coull interval. Pseudocode:</p> <pre><code>float AgrestiCoullLower(int n, int k) { //float conf = 0.05; // 95% confidence interval float kappa = 2.24140273; // In general, kappa = ierfc(conf/2)*sqrt(2) float kest=k+kappa^2/2; float nest=n+kappa^2; float pest=kest/nest; float radius=kappa*sqrt(pest*(1-pest)/nest); return max(0,pest-radius); // Lower bound // Upper bound is min(1,pest+radius) } </code></pre> <p>Then take the lower end of the estimate and sort on this. So the 2/2 is (by Agresti-Coull) 95% likely to fall in the 'helpfulness' range 23.7% to 100%, so it sorts below the 999/1000 which has range 99.2% to 100% (since .237 &lt; .992).</p> <p>Edit: Since some people seem to have found this helpful (ha ha), let me note that the algorithm can be tweaked based on how confident/risk-averse you want to be. The less confidence you need, the more willing you will be to abandon the 'proven' (high-vote) reviews for the untested but high-scoring reviews. A 90% confidence interval gives kappa = 1.95996398, an 85% confidence interval gives 1.78046434, a 75% confidence interval gives 1.53412054, and the all-caution-to-the-wind 50% confidence interval gives 1.15034938.</p> <p>The 50% confidence interval gives</p> <pre><code>1) 999/1000 (99.7%) = 50% likely to fall in 'helpfulness' range of 99.7% to 100% 2) 299/400 (72.2%) = 50% likely to fall in 'helpfulness' range of 72.2% to 77.2% 3) 2/2 (54.9%) = 50% likely to fall in 'helpfulness' range of 54.9% to 100% 4) 3/4 (45.7%) = 50% likely to fall in 'helpfulness' range of 45.7% to 91.9% 5) 1/1 (37.5%) = 50% likely to fall in 'helpfulness' range of 37.5% to 100% </code></pre> <p>which isn't that different overall, but it does prefer the 2/2 to the safety of the 3/4.</p>
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    1. POHow should I order these "helpful" scores?
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    1. POHow should I order these "helpful" scores?
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    1. COFor ties (especially those at 0), I suggest breaking in favor of largest number of upvotes, then smallest number of downvotes.
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    2. COwow, Charles, this is hard core. very impressive. i'll run it on my examples and see how they sort (after i spend a few minutes educating myself on Agresti-Coull at wikipedia!)
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    3. COLet me know how it goes. I can give more information and/or references as needed.
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