Torturing the Data: Mid-Term Elections Implications

 | Nov 15, 2022 09:10AM ET

It’s been tempting in recent weeks to look at the stock market’s performance following US mid-term elections as biased upward for reasons linked to a special factor that prevails after voting. This is probably narrative mining than robust quantitative analysis.

The stock market does, in fact, show an upward bias in the 12-month periods following mid-term elections. The problem is that there are only a handful of mid-term elections in the historical record vs. thousands of 12-month-return windows, which are in fact upward biased. Teasing out why the former are a special subset from the latter due to mid-term elections isn’t obvious, but it makes for great headlines.

Consider how all the S&P 500’s one-year returns stack up since 1952. Clearly, there’s a strong positive skew. The average performance for 18,000-plus one-year returns is +9.1%. Roughly 74% of the one-year results are positive, which means that randomly choosing a handful of data points will likely show gains. Are mid-term election dates something special as start dates for analyzing one-year returns? Maybe, but it’s going to take more than a simple profile of return histories to make that case.