We have analyzed 3D radio source mapping data for a large number of lightning flashes, and found direct evidence that at least 80% of flashes were initiated by a process called a 'fast discharge' or 'fast breakdown'. This supports previous reports that most if not all flashes are initiated this way. Additionally we have conducted a statistical analysis of fast discharge properties. We find that most fast discharges emit only weak radio signals, and on average they are much slower than many previously reported events. We also analyzed electric field measurements associated with fast discharges and found that most could not be detected above instrument noise levels, and those that were detected were also quite weak.