In the last decade, per capita consumption of cigarettes

This argument is what I call a 'guessed cause' argument, which is one of the two most common kinds of arguments in GMAT critical reasoning (the other is a 'prediction/plan' argument).

In a "Guessed Cause," we're noticing some *outcome* and concluding *what must have caused it.* In this story, there's been a huge decline in smoking--we're concluding it's due to the anti-smoking campaign.

There are a few ways to strengthen an argument like this:

1). [Most common] To show that other plausible causes did not occur

2). [Less common] to demonstrate that 'more cause' leads to 'more effect' or 'less cause' leads to 'less effect.' (so in this case, if places where there was more of this anti-smoking messaging saw more of a decrease in smoking, that would strengthen the argument that the messaging was the cause)


So, it helps to keep an open mind about what other possible causes would decrease smoking. One very likely cause would be that cigarettes got more expensive! GMAT CR does rely on basic 'supply/demand' understanding: raise price, lower demand; lower price, increase demand, all else equal.

So an answer that says there was NOT a price increase eliminates that plausible explanation for the decrease in smoking, so it's more likely that the anti-smoking campaign *was* the cause.

You might be thinking "But aren't there still other possible causes?!?" Indeed there are. To strengthen the argument further we could eliminate *those* causes as well. But keep in mind that to *strengthen* an argument does not require *guaranteeing* an argument! We aren't making it *certain* that the anti-smoking campaign caused the decrease, we're just trying to make it *more likely* that it was the cause.