PTCT vs XBI: Correlation
How closely do PTC Therapeutics, Inc. (PTCT) and SPDR S&P Biotech ETF (XBI) trade together? Their weekly returns over three years give a correlation of 0.57, which is moderate.
Data as of 2026-08-27 · refreshed every trading day · weekly returns · methodology
How correlated are PTCT and XBI?
On 3 years of weekly data the PTCT/XBI correlation comes out at 0.57, moderate. Little has changed lately, as the 1-year reading of 0.62 lands near the 3-year figure. The 5-year figure is 0.60, and annualized covariance runs at 825.1 %².
In PTCT's tracked universe of 11 assets, XBI sits right near the top at #1. Their recent paths diverged sharply: over the last 12 months XBI outperformed by 42.9 percentage points (+44.3% for PTCT against +87.2% for XBI). One caveat on sizing: PTCT is 1.9 times as volatile as the other leg, so an equal-dollar split is far from equal-risk.
How is this computed?
Pearson correlation on weekly returns: ρ(A,B) = cov(rA, rB) / (σA · σB), over windows of 52, 156 and 260 weeks. Covariance is annualized (×52) and expressed in %². Full definitions on the methodology page.
PTCT vs XBI: side by side
| PTCT (PTC Therapeutics, Inc.) | XBI (SPDR S&P Biotech ETF) | |
|---|---|---|
| 1-year return | +44.3% | +87.2% |
| 5-year return | +70.4% | +28.6% |
| Volatility (ann.) | 52.5% | 27.7% |
| Beta vs S&P 500 | 1.25 | 1.09 |
| Max drawdown (3Y) | -56.8% | -33.0% |
| Market cap | $6.0B | – |
| P/E (trailing) | – | – |
| Dividend yield | 0.00% | – |
| Sector / category | US Listed | ETF · Thematic |
Year-by-year returns
| Year | PTCT | XBI |
|---|---|---|
| 2022 | -4.2% | -25.9% |
| 2023 | -27.8% | +7.6% |
| 2024 | +63.8% | +1.0% |
| 2025 | +68.3% | +35.9% |
| 2026 | -5.5% | +38.1% |
Calendar-year price returns; the current year is year-to-date as of the data date above.
Are PTCT and XBI good diversifiers for each other?
Somewhat, no more. With 0.57 correlation, most large moves hit both names, and the diversification benefit stays modest.
FAQ
What is the correlation between PTCT and XBI?
Using weekly returns as of 2026-08-27: 0.57 over 3 years, with 0.62 over the last year and 0.60 over 5 years.
Is XBI a good diversifier for PTCT?
Somewhat, no more. With 0.57 correlation, most large moves hit both names, and the diversification benefit stays modest.
What does a correlation of 0.57 mean?
Correlation ranges from −1 to +1. Values near +1 mean two assets move together, near 0 that they move independently, and negative values that they tend to move in opposite directions. It measures co-movement, not performance.
Use this data
$ curl https://www.pairbook.io/api/v1/pairs/ptct-vs-xbi.json
Embed this badge (it refreshes with the data), with attribution:
[](https://www.pairbook.io/pair/ptct-vs-xbi/)
The core API is free. Terms and every endpoint in the API documentation.
Related comparisons
Hubs: PTCT correlations · XBI correlations
