The article introduces a new method to test if a group of related data sets share a common trend over time. Instead of using complicated techniques to remove the influence of other data sets, the researchers suggest a simpler approach. By adding the average values of past data points from each set, they can accurately test for trends without needing to consider how much each set affects the others. The researchers found that this new method works well in practice, as shown by testing it on real exchange rate data and household earnings data.