A certain auto repair shop services a particular make of car in the downtown region of a particular city. Three years ago, 4% of all repairs at this shop were not successful --- the mechanics were not able to restore the car to a drivable state. This year, only 2% of all repairs were not successful. Clearly, the mechanics training course, given over a year ago, has considerably increased the skill of mechanics at this particular shop, so that fewer cars are beyond their ability to repair.
The statement 'Three years ago, statewide smog regulations had the effect of removing the oldest and most unreliable vehicles from the road' does not weaken the argument.