I would include the distance from the hive, and the number of bees that continue the threatening behavior. Any number of things may make them boil out. Larger hives are more defensive, colonys that are on the edge of swarming and fidgity, south winds, or the nectar flow ends abruptly, nighttime visits from the local critters, etc. But if I decide that today really wasn't that bad, and they chase me all the way to shelter, I consider the queens future in doubt.