MDY vs W: Correlation
How closely do SPDR S&P MidCap 400 ETF (MDY) and Wayfair Inc. (W) trade together? Their weekly returns over three years give a correlation of 0.60, which is strong.
Data as of 2026-08-27 · refreshed every trading day · weekly returns · methodology
How correlated are MDY and W?
Over the past 3 years, MDY and W moved with a correlation of 0.60, which is strong. The past 12 months show a weaker link (0.38) than the 3-year average (0.60). Over 5 years the correlation is 0.60, and the annualized covariance of weekly returns is 665.1 %².
Among the 359 assets we track against MDY, W ranks #184 by 3-year correlation. Their recent paths diverged sharply: over the last 12 months W outperformed by 22.7 percentage points (+18.3% for MDY against +41.0% for W). One caveat on sizing: W is 4.1 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 W: side by side
| MDY (SPDR S&P MidCap 400 ETF) | W (Wayfair Inc.) | |
|---|---|---|
| 1-year return | +18.3% | +41.0% |
| 5-year return | +47.5% | -64.0% |
| Volatility (ann.) | 16.5% | 67.1% |
| Beta vs S&P 500 | 0.91 | 2.50 |
| Max drawdown (3Y) | -24.0% | -67.7% |
| Market cap | – | $14.4B |
| P/E (trailing) | – | – |
| Dividend yield | 1.02% | 0.00% |
| Expense ratio | 0.23% | – |
| Assets under management | $26.5B | – |
| Sector / category | ETF · US Small & Mid Cap | US Listed |
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 | MDY | W |
|---|---|---|
| 2022 | -13.3% | -82.7% |
| 2023 | +16.1% | +87.6% |
| 2024 | +13.6% | -28.2% |
| 2025 | +7.2% | +126.6% |
| 2026 | +16.4% | +4.6% |
Calendar-year price returns; the current year is year-to-date as of the data date above.
Are MDY and W good diversifiers for each other?
To a limited degree. At 0.60 the two still catch most of the same waves, so the pair smooths returns a little without insulating either from a shared selloff.
FAQ
What is the correlation between MDY and W?
Using weekly returns as of 2026-08-27: 0.60 over 3 years, with 0.38 over the last year and 0.60 over 5 years.
Is W a good diversifier for MDY?
To a limited degree. At 0.60 the two still catch most of the same waves, so the pair smooths returns a little without insulating either from a shared selloff.
What does a correlation of 0.60 mean?
On the −1 to +1 scale, 0.60 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/mdy-vs-w.json
Embed this badge (it refreshes with the data), with attribution:
[](https://www.pairbook.io/pair/mdy-vs-w/)
No key needed, free to use. Full endpoint list in the API documentation.
Related comparisons
Hubs: MDY correlations · W correlations
