What are the odds of getting a candy when feeding a defending Pokémon in a gym?

As some users have experienced, there is potential to receive a candy of the type corresponding to a Pokémon you feed in any of your team's gyms. This is especially useful to players who haven't been able to amass enough candy to evolve their Chansey or Dratini yet.

I have yet to personally get any candy this way, though, so this is clearly not a guarantee. What is the chance that I get a candy as a bonus for feeding a Pokémon in a gym?

Based on the data produced by this survey for people to submit their personal experiences with candy received to Pokémon fed berries ratio, the rate at which a trainer will receive candies from feeding gym defenders berries is roughly 0.65%.

The current results are 0.65% chance, trainers received 66 candies while feeding 10151 times.