SeasonalCharts.com also offers long term seasonal charts for selected markets as long as adequate data is available. These charts are displayed in the same precise manner, as the shorter-term charts. The chart construction allows for the high variances of price level, for instance a Dow-Jones value of 100 a century ago and today's 10,000-point levels.
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. Die langfristige Saisonalität wird in diesem Fall über einen kürzeren Zeitraum gewissermaßen bestätigt. Freilich kann auch eine solche Saisonalität sich ausgerechnet ab dem Folgejahr wandeln. Dies ist niemals auszuschließen.
In this respect, the combination of long and short term observation is also a kind of test of the stability of seasonality itself, because not only individual years can vary from the seasonal trend. This represents the biggest limit of seasonal analysis (otherwise every price projection would be child’s play with 100% certainty). Seasonality can also change, a common pattern can disappear and new one can emerge.