Apologies for the technical details below! 
The ballot process relies on a pseudorandom number generator (PRNG) and a predetermined seed. 
To summarise from these links:
- A pseudorandom number generator is an algorithm for generating a sequence of numbers whose properties approximate the properties of sequences of random numbers.
- The generated sequence is completely determined by a relatively small set of initial values called the seed.
The secret values are combined and used as the pseudorandom number generator’s seed, and therefore determine the outcome of the ballot. 
The pseurorandom number generator is then used to shuffle the list of pledges, which in turn determines which pledges will be successful.
