Page 40 of the DMG suggests that a large quantity of CR 1 enemies has the potential to challenge a 10th-level party that had lost their equipment. That's an interesting idea, but written kind of vaguely. Like, what the heck is a "large quantity"? Do any of the published materials give more information on the "effective level" that an underequipped (or overequipped) party might amount to?
For example, I'd imagine that at 2nd level, brawlers can find clubs, rangers can throw improvised weapons, and spellcasters tend not to have expensive material components, so a party that gets captured and loses all their gear is at only a moderate disadvantage.
But at 15th level, you're expected to be pretty decked out in magical gear. If this party gets captured, they're going to need significantly weaker enemies to fight for a while. But where is a DM even supposed to start to look when considering what encounter level to face them off against?
Similarly, what about the 2nd-level party that finds a clever solution to a problem, and ends up with items typically meant for 4th-level characters? Or 7th-level characters?
(It wouldn't surprise me if there isn't, like, a table detailing the effective level difference at each level for different percentages of increased/decreased equipment--some classes are affected much more than others, and that would be a lot of information for WotC's designers to consider in general. But if the rules have any additional suggestions for this kind of thing written somewhere, then I'll take whatever they've got!)