If you've been keeping an eye on the state of online games in China, you should know that the Ministry of Culture's new regulations requiring games operating in the region to (among other things) disclose both what rewards can be gained from a game's random "loot box" system and what the odds of getting them are have gone into effect.
That means a bunch of high-profile devs with games in the region have either published (in Chinese) said data or, in the case of Valve with Dota 2, temporarily suspended players' ability to buy "loot box" equivalents in China until they can comply with the new regulations.
Even if you don't have a game in China right now that's affected by these new regulations, it's interesting just to watch and see what data other devs are posting about the drop rates in their games. For example, the Chinese League of Legends website was recently updated with a table of odds for what players can receive when opening the game's "Hextech" loot box equivalents.
The data is in Chinese, but folks on NeoGAF and Reddit have attempted to translate it into English, with varying results. The most popular translation has it that players can receive something like a new skin for a hero about 29.25 percent of the time, but will only see a new hero 7 percent of the time and a new ward icon 2 percent of the time.
However, the same folks raise an interesting question: who can say whether these drop rates, now public information thanks to Chinese regulators, match up at all with the same game's drop rates in other territories?
Well, presumably, the devs could, so we've gone ahead and requested clarification on the matter from Riot Games.