Weaken an Argument Practice Test

A beverage company tested a new label design on its bottled tea in two regions and found that sales in those regions rose by 8% compared with the previous quarter. The company concludes that the new label design increases consumer purchases and decides to roll out the label nationwide. The company notes that the tea’s price and formula were unchanged and that the regions tested are representative of the national market. Which of the following casts the most doubt on the argument?

A public health department concludes that a new advertising campaign caused a recent increase in flu vaccinations. The department notes that in the month after the campaign began, the number of vaccinations administered at local clinics rose by 15% compared with the previous month. The department therefore plans to run the same campaign every year to raise vaccination rates. Which of the following, if true, most weakens the argument?