Train variation

Time to work with US monthly train ridership data! Let's begin by exploring the variation in monthly train ridership. To understand a dataset beyond averages, the variance is an extremely useful statistic. As the name suggests, it gives a sense for the variation that exists in the data. That is, how far from the mean each point is.

As a reminder, to calculate the variance of a population:

1. Calculate the mean of the entire dataset.
2. Subtract each value from the mean.
3. Square the differences to ensure positive and negative values don't cancel each other out.
4. Take the average of the squared differences.

To fully understand variance, in this exercise you will first follow the above steps to calculate the variance manually and then use the VARP() function to automatically calculate variance.