You take 12 trades. Nine are winners. Does that mean you have a 75% win-rate strategy? Probably not. One of the biggest mistakes traders make is drawing conclusions from a sample that is far too small.
Small samples can be deceptive
Suppose you flip a coin ten times and get seven heads. That does not suddenly make the coin 70% heads. Short-term randomness can produce results that look unusually good or unusually bad. Trading is more complicated than a coin flip, but the principle still matters. A few trades rarely provide enough evidence to judge a strategy.
Is 30 trades enough?
Thirty trades are more informative than ten, but still limited. A trader might use an early sample like 30 trades to identify obvious problems, but it is risky to make major conclusions from such a small dataset. The appropriate sample depends on how frequently the strategy trades, how variable the outcomes are, how many different market conditions are represented, and how consistent the rules are.
100 trades is better, but not magic
Traders often use 100 trades as a practical milestone because it provides a much larger dataset than 10 or 20 trades. However, 100 is not a magical statistical threshold. One hundred trades taken during one unusually bullish month may not tell you how the strategy performs during sideways or highly volatile conditions.
Think in terms of both trades and time
A stronger evaluation might include enough trades to reduce the influence of a handful of outcomes, and enough time to include different market environments. A strategy tested across several hundred trades and multiple market conditions generally provides more useful evidence than one evaluated over a few days.
Look for stability
Instead of asking whether your last 100 trades were profitable, compare rolling samples: trades 1 to 50, 51 to 100, 101 to 150, 151 to 200. If profitability exists only in one small segment, that is important. You can also compare win rate, profit factor, expectancy, average win and loss, and drawdown across different samples.
Remove major outliers
Ask what happens if your best trade is removed. Ask what happens if your worst trade is removed. If one trade changes the entire conclusion, your results may not be as robust as they first appear.
Track the data rather than guessing
MyTraderScore can help you analyze your historical results across larger trade samples instead of judging your strategy based on your most recent few wins or losses. The key idea is simple: the fewer trades you have, the less confident you should be in the conclusion.