10nisman, you ask, “Why does the Federal Reserve of St. Louis use the Cass Index?”
Answer: Simple, because it provides the granularity to show the trade volumes in just the St. Louis Fed District. That district is all they are responsible for reporting. Now, St Louis is a fine place to visit in the summer (I spent a week there on day...), some say great ribs, but it sure doesn’t reveal the economic strength (via trade volumes) of the world. Think global not local.