Any question answered...

I'd also say that it depends on the context. If you're talking about 'a set/amount of data', 'data' is often used as shorthand for that, and should either be expanded to the full phrase or used in the singular. If you're clearly talking about multiple items without a clear set-description being implicit, it should be in the plural.

But what if you're talking about olive oil exports in the nineteenth century...? :)

For better or worse, I think the current standard usage is that "data" and "media" are both singular. But I'm not sure whether economics still clings to the more prescriptive usage.