the numbers according to their models, if you believe what they say on their website:
Four major steps
All versions of the model proceed through four major steps:
https://fivethirtyeight.com/features/a-users-guide-to-fivethirtyeights-2016-general-election-forecast/
Step 1: Collect, weight and average polls.
Step 2: Adjust polls.
Step 3: Combine polls with demographic and (in the case of polls-plus) economic data.
Step 4: Account for uncertainty and simulate the election thousands of times.