Credit-card data is broken. Here's how hedge funds and banks are trying to retool one of the original alt-data trades.

· Credit-card data is one of the original alternative-data streams used by hedge funds and other investors.
· But the pandemic has disrupted consumer spending habits, and data vendors have been forced to do more hand-holding with clients.
· Banks are using techniques like post-stratification weighting and "swarming" to help...