MDY vs PRLB: Correlation
SPDR S&P MidCap 400 ETF (MDY) and Proto Labs, Inc. (PRLB) show a moderate relationship: their 3-year correlation of weekly returns is 0.58.
Data as of 2026-08-27 · refreshed every trading day · weekly returns · methodology
How correlated are MDY and PRLB?
Across a 3-year window, the weekly returns of MDY and PRLB correlate at 0.58, moderate. Lately the two have moved closer together, with the 1-year correlation at 0.72 versus 0.58 over 3 years. Stretching to 5 years gives 0.50, with an annualized covariance of 477.9 %².
Among the 359 assets we track against MDY, PRLB ranks #211 by 3-year correlation. The last year tells two different stories: PRLB led by 39.3 percentage points, +18.3% for MDY against +57.6% for PRLB. One caveat on sizing: PRLB is 3.0 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.
MDY vs PRLB: side by side
| MDY (SPDR S&P MidCap 400 ETF) | PRLB (Proto Labs, Inc.) | |
|---|---|---|
| 1-year return | +18.3% | +57.6% |
| 5-year return | +47.5% | +10.1% |
| Volatility (ann.) | 16.5% | 50.3% |
| Beta vs S&P 500 | 0.91 | 1.52 |
| Max drawdown (3Y) | -24.0% | -33.6% |
| Market cap | – | $1.9B |
| P/E (trailing) | – | 62.6 |
| Dividend yield | 1.02% | 0.00% |
| Expense ratio | 0.23% | – |
| Assets under management | $26.5B | – |
| Sector / category | ETF · US Small & Mid Cap | US Listed |
On the fund side, MDY sits in the Mid-Cap Blend category at State Street Investment Management, with $26.5B under management, 400 holdings, a 0.23% expense ratio, a 1.02% trailing dividend yield.
Year-by-year returns
| Year | MDY | PRLB |
|---|---|---|
| 2022 | -13.3% | -50.3% |
| 2023 | +16.1% | +52.6% |
| 2024 | +13.6% | +0.3% |
| 2025 | +7.2% | +29.4% |
| 2026 | +16.4% | +58.3% |
Calendar-year price returns; the current year is year-to-date as of the data date above.
Are MDY and PRLB good diversifiers for each other?
Somewhat, no more. With 0.58 correlation, most large moves hit both names, and the diversification benefit stays modest.
FAQ
What is the correlation between MDY and PRLB?
As of 2026-08-27, the correlation of weekly returns between MDY and PRLB is 0.58 over 3 years, 0.72 over 1 year and 0.50 over 5 years.
Is PRLB a good diversifier for MDY?
Somewhat, no more. With 0.58 correlation, most large moves hit both names, and the diversification benefit stays modest.
What does a correlation of 0.58 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.
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Related comparisons
Hubs: MDY correlations · PRLB correlations
