PRTA vs XBI: Correlation
Measured on weekly returns over the past three years, Prothena Corporation plc (PRTA) and SPDR S&P Biotech ETF (XBI) carry a correlation of 0.55, a moderate link.
Data as of 2026-08-27 · refreshed every trading day · weekly returns · methodology
How correlated are PRTA and XBI?
Over the past 3 years, PRTA and XBI moved with a correlation of 0.55, which is moderate. Recent behaviour matches the longer record: 0.57 over 1 year against 0.55 over 3. Over 5 years the correlation is 0.50, and the annualized covariance of weekly returns is 884.8 %².
Few assets follow PRTA as closely as XBI, which ranks #1 of 11 tracked partners. The last year tells two different stories: XBI led by 81.0 percentage points, +6.2% for PRTA against +87.2% for XBI. Note the risk asymmetry: PRTA runs 2.1 times the annualized volatility of the other leg, so equal-weighting the two is not an equal-risk position.
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.
PRTA vs XBI: side by side
| PRTA (Prothena Corporation plc) | XBI (SPDR S&P Biotech ETF) | |
|---|---|---|
| 1-year return | +6.2% | +87.2% |
| 5-year return | -86.9% | +28.6% |
| Volatility (ann.) | 57.9% | 27.7% |
| Beta vs S&P 500 | 0.93 | 1.09 |
| Max drawdown (3Y) | -91.9% | -33.0% |
| Market cap | $0.5B | – |
| P/E (trailing) | – | – |
| Dividend yield | 0.00% | – |
| Sector / category | US Listed | ETF · Thematic |
Year-by-year returns
| Year | PRTA | XBI |
|---|---|---|
| 2022 | +22.0% | -25.9% |
| 2023 | -39.7% | +7.6% |
| 2024 | -61.9% | +1.0% |
| 2025 | -31.0% | +35.9% |
| 2026 | -4.8% | +38.1% |
Calendar-year price returns; the current year is year-to-date as of the data date above.
Are PRTA and XBI good diversifiers for each other?
Only partially. A correlation of 0.55 means PRTA and XBI share most of their swings. Pairing them dampens volatility somewhat, but it will not protect against a common drawdown.
FAQ
What is the correlation between PRTA and XBI?
As of 2026-08-27, the correlation of weekly returns between PRTA and XBI is 0.55 over 3 years, 0.57 over 1 year and 0.50 over 5 years.
Is XBI a good diversifier for PRTA?
Only partially. A correlation of 0.55 means PRTA and XBI share most of their swings. Pairing them dampens volatility somewhat, but it will not protect against a common drawdown.
What does a correlation of 0.55 mean?
A reading of 0.55 sits on a scale from −1 (opposite moves) through 0 (unrelated) to +1 (identical moves). Correlation captures direction, not magnitude or performance.
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Related comparisons
Hubs: PRTA correlations · XBI correlations
