Good statistics is the key to calendar effects
Many investments show calendar effects like as Santa Claus Rally, January effect, Halloween indicator, October effect. Some of them may be just a coincidences but a lot of them are statistically significant.
Having checked monthly trends of many cases we must say that these calendar effects are not equally strong in the case of each investment. Some of them are very strong (check out the chart below), others may be weaker or completely missing. One can also discover important seasonal tendencies other than the effects mentioned above, regarless on talking about stock market, commodities, forex pairs, indices or mutual funds / ETFs.
Since these effects vary with investments it is better to analyze their effect for each investment separately. This analysis can be made e.g.: per month in a chart like below: