Alpha, Sharpe & Out-of-Sample: How to Read a Backtest Without Being Fooled
Three concepts separate honest indicator research from a curve-fit sales pitch. Here's what they mean — and why we lean on them.
Alpha — vs what?
On this site, 'alpha' means return versus simply buying and holding the same asset. Positive alpha = the indicator beat holding; negative = you'd have done better doing nothing. It's the only benchmark that matters for a single asset, and most indicators are negative on it more often than not.
Sharpe — return per unit of stress
Sharpe is return divided by volatility — reward per unit of risk. A strategy that makes 20% with wild swings can have a worse Sharpe than one that makes 10% smoothly. We rank by Sharpe because raw return rewards luck and leverage; Sharpe rewards consistency.
Out-of-sample — the lie detector
This is the big one. Any indicator can be tuned to look brilliant on past data — that's curve-fitting. We split each asset's history and only trust a result if it held up on the slice the strategy never saw. It's why our numbers look humbler than a course's: we threw out the wins that were just hindsight.
Put together
That's the standard behind all 502,988 backtests here: honest alpha, ranked by Sharpe, validated out-of-sample, with costs. When something clears that bar, it's worth a look. When nothing does, we say 'just hold' — and mean it.
Questions, answered
What is alpha in trading?
Return relative to a benchmark — here, buy-and-hold of the same asset. Positive alpha means the strategy beat holding.
Why is out-of-sample testing important?
It's the guard against curve-fitting — a strategy that only looks good on data it was tuned on isn't an edge, it's hindsight.
Every figure here comes from our own out-of-sample backtests, costs included — not a course or a guess. Educational information only — not investment advice. Hypothetical backtested results; past performance does not guarantee future results. Trading involves risk of loss.
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