Logical reasoning PrepTest 120 · Section 3 · Question 19

Incorrect. Even if this were true, it still doesn't connect diet to heart disease since the stimulus doesn't establish that there's a diet that affects lipoprotein(a) levels.

Incorrect. It does—lipoprotein(a) is correlated with heart disease in people with no other known causes of heart disease.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
Correlation 1 - High cholesterol and heart disease, but it's not 1:1
Correlation 2 - Higher-than-average lipoprotein(a) and heart disease, when no other cause of heart disease is present
Diets that affect cholesterol don't affect lipoprotein(a)
Conclusion - There is no reason to change your diet to prevent heart disease

Answer Anticipation:
This argument is complex and has a large number of correlations and relationships, so we need to be sure that we understand the context that makes them important. And that context always starts with the conclusion.

?Here, the conclusion states that there's no reason to change diet to prevent heart disease. The first thing you should notice about this is that it's very extreme—"no reason." If there's even a hint of a single reason that changing a diet can prevent heart disease, then the conclusion is flawed. We should now be looking at the premises to see where it leaves open the possibility that diet can affect the risk of heart disease.

In those premises, there are two things discussed as being correlated with heart disease—high cholesterol, and higher-than-average lipoprotein(a). And since they're correlated with heart disease, they're potential causes of it. So if diet might affect these levels, then diet might help with preventing heart disease.

Looking at the premise about diet, we see that a diet that affects cholesterol levels won't affect lipoprotein(a) levels. However, that creates two problems for the argument. First, there's no indication there aren't other diets that do affect lipoprotein levels. Second, it establishes that diet can affect cholesterol levels, and the argument never ruled out cholesterol as a contributing factor to some heart disease. While it does show that the relationship between high cholesterol and heart disease isn't 1:1, that doesn't disprove it as a causal factor—there are plenty of causal relationships that don't guarantee the effect based on the cause (think about smoking and lung cancer).

So the argument has two flaws here—it assumes that no diet will affect lipoprotein(a) levels if cholesterol-controlling diets don't, and it assumes that high cholesterol doesn't cause heart disease despite presenting evidence that they're correlated. Either would be a correct answer, so let's see which one shows up.

Answer Explanation:
The argument establishes that there are dietary changes that affect cholesterol levels. The argument also establishes that there is a correlation between high cholesterol levels and heart disease, which is enough to show that there could be a causal relationship between the two. As such, there's reason to believe that dietary changes that lower cholesterol levels will help to prevent heart disease, undermining the conclusion. This answer therefore points out a flaw in the argument.

Key Takeaway:
The more complicated the argument, the more important it is to start your analysis with the conclusion. This will allow you to understand what's out of and in scope, and the role of each statement in proving that conclusion.

Incorrect. First, "poor diets" are out of scope of the argument—what matters are diets that affect certain chemical levels. Second, other health problems are also out of scope since the conclusion is about dietary changes "for the sake of preventing heart disease.

Incorrect. The argument treats high cholesterol as not a causal factor in heart disease since it states there are diets that can lower cholesterol but no reason to follow these diets if you want to prevent heart disease. Explaining why some people with high cholesterol don't develop heart disease would only be necessary in an argument that relies on it being a cause of such disease.