Mean reversion · daily rule · Healthcare
Bollinger Reversion on Boston Scientific
What the play says
BSX with the play, last two years
Shading shows the play's call from the close that triggered it.
Growth of $10,000 since 2005
Log scale. After trading costs, with T-bill interest while out.
The record
The play against buying and holding BSX over exactly the same dates, after costs.
| Play, since 2005 | Hold, since 2005 | Play, 5 yrs | Hold, 5 yrs | |
|---|---|---|---|---|
| Annual return | +2.2% | +1.1% | +2.5% | +0.7% |
| Total return | +60% | +26% | +13% | +4% |
| Worst drawdown | −65.6% | −85.9% | −45.0% | −61.5% |
| Volatility | 20.6% | 32.4% | 17.4% | 26.6% |
| Sharpe ratio | 0.12 | 0.14 | 0.01 | 0.02 |
| Time invested | 25% | 100% | ||
| Switches per year | 9.3 | 0 |
Every call, graded
Right on 133 of 203 closed calls (66%). In calls averaged +0.6%; out calls saw BSX move +0.7% on average.
| Called | Call | Price | Until | BSX moved | Result |
|---|---|---|---|---|---|
| Oct 12, 2026 | OUT | $43.84 | now | −1.2% | open |
| Sep 8, 2026 | IN | $44.98 | Oct 12, 2026 | −2.5% | ✕ wrong |
| Jul 16, 2026 | OUT | $44.62 | Sep 8, 2026 | +0.8% | ✕ wrong |
| May 27, 2026 | IN | $50.46 | Jul 16, 2026 | −11.6% | ✕ wrong |
| May 20, 2026 | OUT | $56.67 | May 27, 2026 | −11.0% | ✓ right |
| Apr 28, 2026 | IN | $58.45 | May 20, 2026 | −3.0% | ✕ wrong |
| Apr 22, 2026 | OUT | $64.87 | Apr 28, 2026 | −9.9% | ✓ right |
| Jan 15, 2026 | IN | $90.03 | Apr 22, 2026 | −27.9% | ✕ wrong |
| Dec 22, 2025 | OUT | $96.43 | Jan 15, 2026 | −6.6% | ✓ right |
| Dec 8, 2025 | IN | $93.84 | Dec 22, 2025 | +2.8% | ✓ right |
| Oct 15, 2025 | OUT | $97.71 | Dec 8, 2025 | −4.0% | ✓ right |
| Sep 15, 2025 | IN | $99.87 | Oct 15, 2025 | −2.2% | ✕ wrong |
An in call is right when the price rose before the next call; an out call is right when it fell. The latest 12 of 204 calls shown.
How the play works
- In on a close below the lower band (20-day average − 2 standard deviations).
- Out on a close above the 20-day average.
This runs against Bollinger's advice that tags of the bands are not signals. It is shown because so many traders use it.
The case against
Valeriy Zakamulin tested moving-average timing on up to 155 years of U.S. stock data and found no statistically significant edge in the second half of that record. The rules earned their keep in a few severe bear markets and lagged buy and hold for long stretches in between.