The benefit of a long-term view lies in its statistical importance. A seasonal pattern that appears over a period of many years has higher statistical relevance than a pattern appearing over a shorter time frame. Additionally there is less influence from single extreme years.
But also important is the fact that seasonality can transform over time, for instance because of technological development. That’s why the actuality of a seasonal chart is also an important factor that must be guaranteed along with statistical relevance, which is why short-term seasonal trends should also be examined.
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