Presidential Election Cycle (Theory)

What Does Presidential Election Cycle (Theory) Mean?
A theory developed by Yale Hirsch that states that U.S. stock markets are weakest in the year following the election of a new U.S. president. According to this theory, after the first year, the market improves until the cycle begins again with the next presidential election.

Investopedia explains Presidential Election Cycle (Theory)
While the theory played out relatively reliably in the early to mid 1900s, data from the later twentieth century has disproved it. 

In 1937, Franklin D. Roosevelt's first year, the market was down by 27.3%. The Truman and Eisenhower eras also started off with a down year in the stock market. The start of more recent presidencies, however, did not show the same pattern. In George H.W. Bush's first year, the market was up 25.2%, and the start of both of Bill Clinton's terms showed strong market performance - up by 19.9% and 35.9%.