Mean reversion · daily rule · Healthcare
Bollinger Reversion on Intuitive Surgical
What the play says
ISRG 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 ISRG over exactly the same dates, after costs.
| Play, since 2005 | Hold, since 2005 | Play, 5 yrs | Hold, 5 yrs | |
|---|---|---|---|---|
| Annual return | +10.9% | +23.6% | +9.3% | +5.3% |
| Total return | +847% | +9,968% | +55% | +29% |
| Worst drawdown | −38.4% | −75.9% | −26.8% | −49.9% |
| Volatility | 21.3% | 39.8% | 20.8% | 34.6% |
| Sharpe ratio | 0.51 | 0.68 | 0.35 | 0.21 |
| Time invested | 22% | 100% | ||
| Switches per year | 9.1 | 0 |
Every call, graded
Right on 127 of 198 closed calls (64%). In calls averaged +2.3%; out calls saw ISRG move +4.1% on average.
| Called | Call | Price | Until | ISRG moved | Result |
|---|---|---|---|---|---|
| Sep 14, 2026 | OUT | $377.94 | now | +11.7% | open |
| Sep 8, 2026 | IN | $350.16 | Sep 14, 2026 | +7.9% | ✓ right |
| Aug 3, 2026 | OUT | $375.41 | Sep 8, 2026 | −6.7% | ✓ right |
| Jul 14, 2026 | IN | $379.50 | Aug 3, 2026 | −1.1% | ✕ wrong |
| Jul 2, 2026 | OUT | $426.01 | Jul 14, 2026 | −10.9% | ✓ right |
| May 11, 2026 | IN | $420.06 | Jul 2, 2026 | +1.4% | ✓ right |
| Apr 14, 2026 | OUT | $467.22 | May 11, 2026 | −10.1% | ✓ right |
| Mar 13, 2026 | IN | $472.16 | Apr 14, 2026 | −1.0% | ✕ wrong |
| Feb 20, 2026 | OUT | $504.05 | Mar 13, 2026 | −6.3% | ✓ right |
| Jan 14, 2026 | IN | $546.76 | Feb 20, 2026 | −7.8% | ✕ wrong |
| Sep 30, 2025 | OUT | $447.23 | Jan 14, 2026 | +22.3% | ✕ wrong |
| Jul 24, 2025 | IN | $488.61 | Sep 30, 2025 | −8.5% | ✕ 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 199 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.