PRTA vs SPRO: Correlation
How closely do Prothena Corporation plc (PRTA) and Spero Therapeutics, Inc. (SPRO) trade together? Their weekly returns over three years give a correlation of -0.24, which is negative.
Data as of 2026-08-27 · refreshed every trading day · weekly returns · methodology
How correlated are PRTA and SPRO?
On 3 years of weekly data the PRTA/SPRO correlation comes out at -0.24, negative, meaning they tend to move in opposite directions. The link has tightened recently: the 1-year correlation (0.15) runs above the 3-year figure (-0.24). The 5-year figure is -0.07, and annualized covariance runs at -2205.0 %².
Out of 11 assets tracked against PRTA, SPRO lands near the bottom at #9. Their recent paths diverged sharply: over the last 12 months PRTA outperformed by 45.1 percentage points (+6.2% for PRTA against -38.9% for SPRO). Risk is not evenly split, since SPRO carries 2.8 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 SPRO: side by side
| PRTA (Prothena Corporation plc) | SPRO (Spero Therapeutics, Inc.) | |
|---|---|---|
| 1-year return | +6.2% | -38.9% |
| 5-year return | -86.9% | -93.3% |
| Volatility (ann.) | 57.9% | 159.8% |
| Beta vs S&P 500 | 0.93 | 1.61 |
| Max drawdown (3Y) | -91.9% | -68.9% |
| Market cap | $0.5B | $0.1B |
| P/E (trailing) | – | 8.6 |
| Dividend yield | 0.00% | 0.00% |
| Sector / category | US Listed | US Listed |
Year-by-year returns
| Year | PRTA | SPRO |
|---|---|---|
| 2022 | +22.0% | -89.2% |
| 2023 | -39.7% | -15.0% |
| 2024 | -61.9% | -29.9% |
| 2025 | -31.0% | +126.2% |
| 2026 | -4.8% | -48.1% |
Calendar-year price returns; the current year is year-to-date as of the data date above.
Are PRTA and SPRO good diversifiers for each other?
Yes: at -0.24, the two have gone their own ways historically, which is what genuine diversification looks like.
FAQ
What is the correlation between PRTA and SPRO?
As of 2026-08-27, the correlation of weekly returns between PRTA and SPRO is -0.24 over 3 years, 0.15 over 1 year and -0.07 over 5 years.
Is SPRO a good diversifier for PRTA?
Yes: at -0.24, the two have gone their own ways historically, which is what genuine diversification looks like.
What does a correlation of -0.24 mean?
On the −1 to +1 scale, -0.24 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.
Use this data
$ curl https://www.pairbook.io/api/v1/pairs/prta-vs-spro.json
Drop this badge in a README or notebook; it updates with the data:
[](https://www.pairbook.io/pair/prta-vs-spro/)
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Related comparisons
Hubs: PRTA correlations · SPRO correlations
