A ward office banned parking along the eastern side of the market street and reports that the vehicles standing on that side have fallen from about ninety to none. It concludes that the ban has cut the number of vehicles brought into the market area. Which of the following, if true, most weakens the ward office's conclusion?

The ninety vehicles have not stopped coming; they have gone round the corner, and a count at the mouths of the market shows as many entering as ever. The ban emptied one kerb and filled two lanes, which is a change of place and not a change of number. Who enforces the ban and how much notice was given describe how it was brought in; the absence of a count on the western side points to a gap in the figures without showing what filled it, whereas the rear lanes show where the ninety went.