The post-COVID bars average three years. The first, when the winter quarter was unusually weak, fell outside the range expected from the pre-COVID years; the next two fell inside it.
What this shows: The chart plots Average of 2015 to 2019 (pre-COVID) and Average of 2022 to 2024 (post-COVID) on a vertical axis of Quarter’s traffic against its year’s average (1.0 = average).
Conditions and method
Status: descriptive (a pattern in the data, not a causal estimate).
Each post-COVID year is checked against the pre-COVID range (2015 to 2019): the interval that a further year like those would fall inside 95% of the time, on the first-quarter ratio and the Q3-Q1 swing. In 2022 the first-quarter ratio is below the range and the Q3-Q1 swing is above the range; 2023 and 2024 are inside on both. On the narrower span from the lowest to the highest of the pre-COVID years’ own values, 2023 on the first-quarter ratio and 2024 on the Q3-Q1 swing also fall outside. The post-COVID bars average all 3 years, 2022 included.
The break test compares the whole seasonal regression, trend included, before and after the break, so its rejection of stability does not by itself say the seasonal pattern is still shifted.