The formula to calculate the seasonal index (SI) is:
\[ SI = \left( \frac{S}{A} \right) \times 100 \]
Where:
A Seasonal Index is a statistical tool used to measure and quantify the recurring patterns or variations in data that occur regularly within a year. It is often used in sales forecasting, economic forecasting, and inventory management to account for seasonal fluctuations like holiday shopping or seasonal weather changes. The index provides a numerical value that helps in adjusting data to reflect the relative period-to-period changes due to seasonality.