SPX, based on the short week after Labor day(Friday close vs before-Labor-Day-close, some days could be up or down), this year(2024) was the worst since 1950(no data available before then). Those were the years with 2% or more down.
2024 -4.25
2001 -4.22
2008 -3.16
2020 -2.51
2002 -2.42
2016 -2.4
Example, for 2024, it's today's close(5,408.42) / Aug 30 close(5,648.4) = -4.25%
for 2023, it's 4,457.49(from Sep 8, 2023) / 4,515.77(from Sep 1, 2023) = -1.3%