Passage Summary: A columnist argues that because smoking rates fell after ads were banned, the ads must have been the reason people were smoking in the first place.

Conclusion: Tobacco companies are wrong to claim that advertising does not have a significant causal effect on the decision to smoke.

Reasoning: Countries that have implemented strict bans on tobacco advertising have seen a notable decrease in the number of people who smoke.

Analysis: The columnist is inferring a causal relationship from a simple correlation. To weaken this, we need to find an alternative cause for the decline in smoking that occurred at the same time as the ad bans. If these countries also raised cigarette taxes or launched health education programs, the ad ban might just be a bystander to the real cause of the decline. Look for an answer that introduces a third variable that explains the drop in smoking rates.