October marks the start of the fourth quarter and the end of the worst six-month time frame in which to own stocks. That implies November and December are usually kind to the bulls. With the S&P 500 up 3.3% so far in October, stocks could be poised to rally into year-end.

Investors may want to consider the odds of a fourth-quarter rally because history says that when September is a strong month for stocks, the good times continue in the final quarter of the year. The S&P was solid last month.

“Historically, strong Septembers lead to strong fourth quarters (up 5.12% on average, vs. 2.04% for all years since 1926), with much of the outperformance occurring in October & November. The S&P 500 rose just under 3% this September,” said Piper Jaffray Managing Director Craig Johnson in a research note.

There are 20 instances since 1926 of the S&P 500 notching positive fourth-quarter performances with a median gain of 5.22% following a September gain of 3% or more, according to Piper Jaffray Technical Research.

At the sector level, financial services and energy have been laggards in the fourth quarter on an unweighted basis since 1969, Piper Jaffray data show. However, that does not mean investors should run out and short the Financial Select Sector SPDR (NYSEArca: XLF) or the iShares U.S. Energy ETF (NYSEArca: IYE). Those sectors traditionally rise in the fourth quarter, just not as much as rival groups. [FAS/FAZ Debate]