Variance
The natural swing in results around your expected outcome. Even a profitable strategy produces losing streaks because of variance.
Variance is why a real edge can still feel like losing for stretches, and why sizing matters: bet too big and variance alone can ruin you before the edge plays out. Separating variance from genuine skill or leak is a core analytics task.
Variance is the natural swing of results around their expected average. Because trading outcomes are probabilistic, even a strategy with a real edge will string together wins and losses that look nothing like its long-run average over short stretches. Variance is the reason a profitable approach can lose for weeks and a losing one can win for a while.
The danger of variance is psychological and financial. It tempts traders to abandon a sound strategy during a normal cold streak, or to credit a flawed one during a lucky hot streak. It also threatens undersized bankrolls, because a run of losses well within normal variance can still exhaust capital that was sized too aggressively.
You cannot eliminate variance, only manage it. Larger sample sizes pull realized results toward expected value, and smaller position sizes keep variance from threatening survival. Separating variance from edge, distinguishing bad luck from a bad strategy, is one of the hardest and most valuable skills in trading.
A coin-flip edge that wins 55 percent of the time will still produce losing streaks of five or six in a row fairly often. Those streaks are variance, not evidence the edge is gone, which is why judging a strategy requires a large sample, not a handful of trades.
Frequently asked questions
What is variance in trading?
It is the swing of actual results around their expected average. Over short periods, even an edge-positive strategy can lose and an edge-negative one can win, purely from chance.
How do I tell variance from a broken strategy?
By sample size and calibration. Short losing streaks are usually variance; a large sample where your results consistently lag your expected edge suggests a real problem. One bad week is rarely conclusive.
How do I manage variance?
Trade enough volume for results to converge toward expected value, and size positions small enough that a normal losing streak cannot threaten your bankroll.