CERS vs MDY: Correlation
How closely do Cerus Corporation (CERS) and SPDR S&P MidCap 400 ETF (MDY) trade together? Their weekly returns over three years give a correlation of 0.55, which is moderate.
Data as of 2026-08-27 · refreshed every trading day · weekly returns · methodology
How correlated are CERS and MDY?
On 3 years of weekly data the CERS/MDY correlation comes out at 0.55, moderate. The link has loosened recently: the 1-year correlation (0.36) runs below the 3-year figure (0.55). The 5-year figure is 0.51, and annualized covariance runs at 644.7 %².
In CERS's tracked universe of 10 assets, MDY sits right near the top at #2. The last year tells two different stories: CERS led by 89.3 percentage points, +107.6% for CERS against +18.3% for MDY. One caveat on sizing: CERS is 4.3 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.
CERS vs MDY: side by side
| CERS (Cerus Corporation) | MDY (SPDR S&P MidCap 400 ETF) | |
|---|---|---|
| 1-year return | +107.6% | +18.3% |
| 5-year return | -57.3% | +47.5% |
| Volatility (ann.) | 71.0% | 16.5% |
| Beta vs S&P 500 | 2.01 | 0.91 |
| Max drawdown (3Y) | -52.1% | -24.0% |
| Market cap | $0.5B | – |
| P/E (trailing) | – | – |
| Dividend yield | 0.00% | 1.02% |
| Expense ratio | – | 0.23% |
| Assets under management | – | $26.5B |
| Sector / category | US Listed | ETF · US Small & Mid Cap |
MDY, State Street Investment Management's Mid-Cap Blend fund, carries $26.5B under management, 400 holdings, a 0.23% expense ratio, a 1.02% trailing dividend yield.
Year-by-year returns
| Year | CERS | MDY |
|---|---|---|
| 2022 | -46.4% | -13.3% |
| 2023 | -40.8% | +16.1% |
| 2024 | -28.7% | +13.6% |
| 2025 | +33.8% | +7.2% |
| 2026 | +32.0% | +16.4% |
Calendar-year price returns; the current year is year-to-date as of the data date above.
Are CERS and MDY good diversifiers for each other?
Somewhat, no more. With 0.55 correlation, most large moves hit both names, and the diversification benefit stays modest.
FAQ
What is the correlation between CERS and MDY?
Using weekly returns as of 2026-08-27: 0.55 over 3 years, with 0.36 over the last year and 0.51 over 5 years.
Is MDY a good diversifier for CERS?
Somewhat, no more. With 0.55 correlation, most large moves hit both names, and the diversification benefit stays modest.
What does a correlation of 0.55 mean?
On the −1 to +1 scale, 0.55 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
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Related comparisons
Hubs: CERS correlations · MDY correlations
