PRTA vs SPY: Correlation
Measured on weekly returns over the past three years, Prothena Corporation plc (PRTA) and SPDR S&P 500 ETF Trust (SPY) carry a correlation of 0.23, a weak link.
Data as of 2026-08-27 · refreshed every trading day · weekly returns · methodology
How correlated are PRTA and SPY?
Over the past 3 years, PRTA and SPY moved with a correlation of 0.23, which is weak. The past 12 months show a weaker link (0.10) than the 3-year average (0.23). Over 5 years the correlation is 0.18, and the annualized covariance of weekly returns is 194.3 %².
Within PRTA's tracked universe of 11 assets, SPY comes in at #6 by 3-year correlation. The trailing year gives SPY the advantage: +6.2% versus +20.6%, a 14.4-point spread. Risk is not evenly split, since PRTA carries 4.0 times the volatility of the other side.
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 SPY: side by side
| PRTA (Prothena Corporation plc) | SPY (SPDR S&P 500 ETF Trust) | |
|---|---|---|
| 1-year return | +6.2% | +20.6% |
| 5-year return | -86.9% | +82.4% |
| Volatility (ann.) | 57.9% | 14.5% |
| Beta vs S&P 500 | 0.93 | 1.00 |
| Max drawdown (3Y) | -91.9% | -18.8% |
| Market cap | $0.5B | – |
| P/E (trailing) | – | – |
| Dividend yield | 0.00% | 1.01% |
| Expense ratio | – | 0.09% |
| Assets under management | – | $795.3B |
| Sector / category | US Listed | ETF · US Large Cap |
SPY is a Large Blend fund from State Street Investment Management: $795.3B under management, 504 holdings, a 0.09% expense ratio, a 1.01% trailing dividend yield.
Year-by-year returns
| Year | PRTA | SPY |
|---|---|---|
| 2022 | +22.0% | -18.2% |
| 2023 | -39.7% | +26.2% |
| 2024 | -61.9% | +24.9% |
| 2025 | -31.0% | +17.7% |
| 2026 | -4.8% | +13.7% |
Calendar-year price returns; the current year is year-to-date as of the data date above.
Are PRTA and SPY good diversifiers for each other?
Yes, to a useful degree: a correlation of 0.23 leaves real independence between the two, which historically damped combined volatility.
FAQ
What is the correlation between PRTA and SPY?
The PRTA/SPY correlation stands at 0.23 on a 3-year window (1 year: 0.10, 5 years: 0.18), computed from weekly returns as of 2026-08-27.
Is SPY a good diversifier for PRTA?
Yes, to a useful degree: a correlation of 0.23 leaves real independence between the two, which historically damped combined volatility.
What does a correlation of 0.23 mean?
On the −1 to +1 scale, 0.23 describes how much the two returns move together: +1 is lockstep, 0 is independence, negative values mean opposite directions. It says nothing about which performed better.
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Related comparisons
Hubs: PRTA correlations · SPY correlations
