#21 - People with higher-than-average blood levels of a

[ericj_williams]

Could you help me understand why D would be incorrect if seen as an alternate cause?

D seems to imply it is actually genetic vs caused by homocysteine. At least that's how I saw it.

Re-reading I can see that D a little more "off-topic" that E, which contains two key terms of the stimulus.

[Meshal Alotaibi]

Hi, the conclusion has risk of "developing" language, why would E be relevant if the disease exists, or is that a wrong interpretation option E? In other words, assuming that the disease is not there, the higher-than-average level would indicate that the risk of development is high, and the author argues that reducing the levels of H would help in reducing the risk of the disease. Option E instead is saying that the disease increases it, but that's besides in the point. I choose option B even those its language is weak in that it uses "can... sometimes." Thanks

[Luke Haqq]

Hi Meshal!

This stimulus identifies a specific causal relationship. It indicates that homocysteine is the cause and the effect is Alzheimer's disease.

In general, there are several ways to weaken cause and effect claims. For example, one could show the existence of the cause without it leading to the effect, or show that the cause and effect relationship is instead reversed. Answer choice (E) does the latter; rather than homocysteine causing Alzheimer's, it suggests that the cause and effect relationship is reversed, with Alzheimer's causing homocysteine levels to rise.

Answer choice (B) doesn't get to the conclusion. The conclusion is that "it is likely that the risk of developing Alzheimer’s disease could be reduced"--the risk in the conclusion is just about Alzheimer's disease and nothing else. Even if the mentioned conversion process had other harmful effects, it could still reduce the risk of developing Alzheimer's.

[flowerpower]

Hi! Is (D) wrong because the alt cause provided (genetics) doesn't necessarily preclude the B vitamins from having a causal effect on Alzheimer's? Does an alt cause weaken a causal claim?

[flowerpower]

Sorry, I missed Brook's comment above about (D). Let me refine my question: when faced with a causal weaken question, should we be looking first for 1) no cause, effect; 2) cause, no effect; and 3) effect causes cause, and then look for an alternative cause to weaken if we can't find any of those first 3?

[Jeff Wren]

Hi flower,

In most Weaken questions involving "typical" causal arguments with only one cause, the correct answer is usually:

1. an alternate cause
2. the cause without the effect
3. the effect without the cause
4. attacking the data
5. showing that the cause and effect are reversed

Generally in that rough order. Showing that the causal relationship is the reversed doesn't usually make sense in most causal arguments and would be inapplicable, but it does occur from time to time, like in this question.

However, with arguments involving partial causes or multiple causes, then answers providing alternate causes do not necessarily weaken the argument.

Here, we know that above average levels of homocysteines are correlated with a higher likelihood of being diagnosed with Alzheimer's disease, but there is no indication that this is the one and only cause of Alzheimer's disease. Answer D is completely consistent with the conclusion in the argument.

For example, even if people who have family members with obesity are more likely to develop obesity, that does not mean that certain behaviors (such as diet and exercise) cannot reduce an individual's likelihood of developing obesity.

Rather than rely on a specific order, simply examine each answer to see if it weakens the argument (especially if it is one of these five ways for a causal argument) and then decide which answer is best based on the specific details in the argument.