SPX up 15 of 17 weeks (does it matter?)

Key points

• The S&P 500 closed higher in 15 of the last 17 weeks
• This fact is being heavily touted on social media
• But the relevant question is, "Does it matter?"

The S&P 500 has enjoyed a terrific run

As of the week ending 2024-02-23, the S&P 500 closed higher in 15 of the last 17 weeks, as shown in the chart below.

This is an infrequent occasion - as seen in the chart below. This has not happened since 1989.

The chart above (or similar) has been touted widely on social media this week. Interestingly, some claim it is bullish, and others claim it is not. While this is an interesting development and seems significant, the real question is, "Does it matter?"

Setting the baseline

The table below summarizes S&P 500 performance for 1, 2, 3, 4, 8, 13, 26, 39, and 52 weeks considering all weeks starting on 1920-04-30. 

Looking only at "15 of 17 Up Weeks"

Let's look only at weeks that met the "15 of 17 Up Weeks" criteria. The table below displays all dates and S&P 500 performance when these criteria were met.

The table below summarizes S&P 500 performance following "15 of 17 up weeks" AND how these results compare to All Weeks.

The bottom line is "mixed results." Some periods have shown better performance and higher Win Rates than All Weeks; others have shown worse. The bottom line is that anyone touting the latest 15 of 17 Up Weeks occurrence on 2024-02-23 as a decidedly "bullish" or "bearish" omen has probably not seen this data.

Using the "15 of 17 UP Weeks" anomaly systematically

Before writing off 15 of 17 Weeks as "not terribly significant," let's take one more pass at using this event. The method below uses the following "Rules":

• If SPX has closed higher for at least 15 of the last 17 weeks, buy and hold the S&P 500 Index for 39 weeks
• If during this initial 39 weeks, another "15 of 17 Up Week" occurs, extend the holding period for another 39 week

The equity curve displays the growth of $1 invested using this approach.

The table below shows the "trades" and summarizes the results of systematically using the rules above.

What the research tells us…

Is there value in noting when the S&P 500 closes higher for at least 15 of 17 weeks? That is for each individual to decide for themselves. We can state with some certainty that not every market anomaly posted on social media "means what someone says it means."