Hi guys,

received a pm asking me to post.

This is a classic causal argument. The author's evidence establishes a correlation between two things. A correlation can arise in one of two ways on the GMAT (and in real life):

1)Temporally: either A precedes B (or B precedes A); or

2)Simultaneously: A and B occur together.

The author then uses the correlation to conclude a relationship of causation exists between those two things, ie, either A causes B or the other way around.

The necessary assumption in all of these arguments is that there are no other causes. This is a necessary assumption because if there were another cause, then the author's claim of causation is not necessarily correct.

If this were a weaken question, then we would find an answer choice that would attack this assumption.

The most common way this assumption gets attacked is an answer choice suggesting that there is some other cause.

A very common way it gets strengthened is an answer choice negating another cause. Once an alternative explanation has been removed, it is more likely that the cause argued for by the author is the real cause. (And because it is more likely, it is strengthened).

Strategically, a great thing to do here is to use the Kaplan denial test. In a strengthen question, if you have an answer choice you are unsure about, then deny the choice. If the argument is now (after denial of the choice) clearly weakened, then this is the correct answer. And a good time to do it is when you are in a strengthen question, and you have a choice you are not sure about. Another good indicator is if the answer choice uses words like "not" or "no".

Let's apply all this to this question.

Step one of the Kaplan method: Read the stem. Okay, so it is a strengthen question.

Step two: analyze the passage stimulus:

We have a correlation between taxes (A) and greater dip in cigarette sales (B). Does this establish that the taxes caused the dip in sales?

Nope.

Yet, that is what the author is concluding. So, he is assuming there are no other causes.

Step three: make a prediction. Say to yourself: "The assumption is no other causes. This is a strengthen question. I need to find an answer choice that backs this assumption up. I will look for a choice that negates a possible alternative cause (takes away an alternative explanation) for the drop in cigarette sales. An answer choice that says that the drop in cigarette sales wasn't due to something else."

Step four: Aggressively scan for a match:

Choice A: Definitely a weakener, nix

Choice B: hmmm "information about smoking health problems unchanged". This is negative language ("unchanged"), let's deny this. What if the information available about smoking health problems DID change. Well, they can't take information away, so if the information changed, then more people would know more facts about smoking health problems.

That could clearly be an alternative explanation for why cigarette sales went down. It wasn't the taxes, instead it could have been increased awareness of the health evils of smoking.

Because the denial of B clearly weakens, choice B is the correct answer to the strengthen question.


Notice that because we have found a match to our prediction, there is no need to evaluate the remaining answer choices. We got the light bulb when we read choice B. And, if we still weren't quite sure, verifying our reasoning for choice B's being correctness is far better (ie, quicker, more score-maximizing) than drowning in the indeterminate murkiness of all the trap answer choices. Predicting and matching to the right answer is better than coming up with four reasons for why the four wrong answers are wrong.

Hi nervesofsteel,

Yes, that would be an assumption on our part. We would have to assume that because of knowledge of the tax hike, they stocked up cigarettes beforehand. But what if they don't have enough money to do that? (After all, these are the same people who are going to stop buying because of the tax increase.) Or, what if the cigarettes went stale inside of six months, or three months, or two months, or...oh, I'm sure you get it.

As an aside, we need not use the denial test to see that choice B is correct; we can do it directly.

The assumption: there are no other causes

How to strengthen? by backing up the assumption.
In other words, find an answer choice that suggests that something else wasn't the cause of cigarette sales drop.

What does choice C do? removed a possible alternative causes for the cigarette sales decline: that people were better informed about the health problems associated with cigareetre smoking.

[I understand why A is a weakener. But, for A to be a weakener we have to assume that sales volume will remain low foreever after the sales tax increase ?

If sales volume go back to normal levels, which is what stated in A, then that shows a correlation between sales tax increase and decreased sales volume.]