Calculate 3-month centered moving average

To calculate a 3-month centered moving average, first, take the average of the data points for each month, including the month before and the month after. For example, for the month of January, you would average the values of December, January, and February. This process is repeated for each month in the dataset, resulting in a smoothed series that better reflects trends over time. The centered aspect means that the average for each month is aligned with the middle month of the three being averaged.