The annual Sharpe ratio hides an assumption about your returns
Annualising a monthly Sharpe ratio by multiplying by the square root of twelve is not a unit conversion. It is Andrew Lo...
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A distress-zone Z-score does not mean a 70% chance of bankruptcy
The Altman Z-score's famous 70% is the share of firms that DID fail which had scored in the distress zone — a sensitivit...
Why Your Best Performers Get Worse
A thousand simulated pages whose true conversion rates never change. Selected on one period's numbers, the top tenth app...
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What Happens When You Test Twenty Metrics
A dashboard rarely shows one number. Simulated with nothing real to find, examining twenty metrics produced at least one...
How Big Does an A/B Test Need to Be?
Sample size is usually decided by how long someone will wait. Simulated across a grid, a genuine one-point lift on a ten...
What Happens When You Check an A/B Test Early
Twenty thousand simulated experiments with no real difference in them. Read once at the end, 4.9% came back significant,...
Grades, GPAs and What They Convert To
NUS publishes separate grade profiles for A-level and polytechnic applicants, and none at all for IB — because, it says,...
Kati, Tahil, Cups and Grams
Ask for a catty of pork and you get 500 g in Guangzhou, 600 g in Taipei and 604.8 g in Singapore — all three legally cor...
Mean, Median, Mode: The Average Is a Choice, Not a Fact
Three different numbers are all correctly called "the average", and which one gets published changes what a reader concl...
A High R² Does Not Mean the Model Is Right
Anscombe printed one regression summary for four data sets in 1973 and said the features that matter are "invisible if w...
Standard Deviation vs Standard Error: Two Numbers, Two Questions
Mean ± 4.36 and mean ± 0.97 are not two ways of saying the same thing. Altman and Bland assigned each to a different que...
What a 95% Confidence Interval Actually Means
Nearly everyone reads a confidence interval as "there is a 95% probability the true value is in here" — including 59% of...
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