Historical analysis is useful because it replaces vague impressions with measurable observations. Its weakness is equally important: the market regime, company structure and macro backdrop can change, so past results must be treated as context rather than certainty.
When researching a recurring seasonal period, calculate the same window for each eligible year. Then study the full distribution instead of compressing everything into one average.
Useful summary, but vulnerable to extreme observations.
Shows the middle historical result and helps reveal whether the average is distorted.
Shows frequency, which should be considered separately from return magnitude.
A company can change dramatically over 20 years. Index composition changes too. A historical tendency that existed under one regime may weaken under another.
If you test hundreds of date windows, some will look impressive by chance. Predefine the question where possible and compare nearby windows or multiple lookbacks.
A pattern with a positive average can still contain deep negative years. Looking at every observation makes the risk visible and helps distinguish a broad tendency from a result driven by one or two outliers.
Comparing 10, 15 and 25 years can reveal whether the pattern is stable or dependent on a narrow period.
Select a ticker and dates in the free dashboard to review the historical path and individual yearly results.