Correlations and Causal Reasoning on the LSAT

The makers of the LSAT frequently create arguments that conflate correlation with causation.

It’s very important to understand the distinction between the two, and we’ll explain it all in this article.

In statistics, "correlation" refers to a statistical relationship between two interdependent variables (e.g. height and weight, studying and grades, etc.). A correlation alone does not prove a causal relationship, but it can suggest that a causal relationship does, in fact, exist. For instance, a correlation between height and weight cannot be interpreted to mean that either one causes the other. On the other hand, a correlation between studying and grades implies that studying causes higher grades, but the correlation alone is not sufficient to prove that such a causal relationship exists.

An empirically observable correlation between two interdependent variables is a necessary, but not sufficient, condition for causality.

On the LSAT, correlations usually function as evidence presented in support of a causal conclusion:

Premise: A and B are correlated

Conclusion: A causes B

Usually, the problem with such arguments is the presumption that correlation proves causation. It does not, as there could be some third factor that could explain (i.e. provide a causal explanation for) the observed correlation, or other means of interpreting the relationship.

Here's an example of a typical causal argument involving a correlation:

Scientists have long suspected that isoflavones, a class of biologically active organic compounds, tend to improve one's cognitive performance. Now these views have acquired strong support from a recent study showing that college students who took soy isoflavone supplements for 3 months did significantly better on various reasoning tasks than students who never took such supplements.

The structure of the argument is as follows:

Premise: Soy isoflavone supplementation is correlated with improved cognitive performance.

Conclusion: Soy isoflavone supplementation causes an improvement in cognitive performance.

When analyzing such arguments, it is important to consider why the correlation observed may not be sufficient to establish the causal conclusion. The problem is usually with the way in which the study was controlled. For instance, if the students examined were not randomly assigned to each group, this would imply a selection bias in the experimental group and compromise the validity of the conclusion. Indeed, if those who are particularly driven or ambitious tend to take performance-enhancing supplements, and also tend to do better on various reasoning tasks than their less ambitious counterparts, the correlation between isoflavone supplementation and performance could be explained by a third factor (ambition) causing both the alleged “cause” and the “effect.”

To eliminate the possibility of bias, it may also be important to conduct a double-blind study in which neither the students nor the researchers know who belongs to the control group and who belongs to the experimental group until after all data have been recorded. Without a double-blind study, it is possible that the correlation observed is a function of a placebo effect, or of the experimenters’ own subjective bias towards the expected result.

Arguments that follow this pattern of reasoning are typically followed by one of the following question types:

Weaken
Strengthen
Assumption
Flaw in the Reasoning

How exactly does the LSAT exploit the subtle difference between correlations and causations in Weaken questions?

Here is a typical stimulus containing a causal conclusion supported by a correlation:

Pump3D is a nutritional supplement that can greatly reduce athletes’ fatigue after anaerobic exercise. This was shown by a study investigating the relationship between fatigue and high doses of guarana extract—the main ingredient in Pump3D—which showed that people who regularly take guarana extract supplements have a significantly lower level of fatigue after anaerobic exercise than people who do not take the supplement.

Since the key to weakening an LSAT argument is to focus on the conclusion, it is essential to break down the argument. The conclusion is the first sentence in the stimulus, in support of which the author describes the results of one particular study (“this is shown by” is a premise indicator):

Premise: People who regularly take guarana extract supplements have a significantly lower level of fatigue after anaerobic exercise than people who do not take the supplement.

Premise: Guarana extract is the main ingredient in Pump3D.

Conclusion: Pump3D can greatly reduce athletes’ fatigue after anaerobic exercise.

The advertisement’s conclusion is based on a questionable assumption, since the study only establishes a correlation between lower level of fatigue and guarana supplementation. While there are many ways of attacking the conclusion, most will require undermining the reliability of the study or experiment. First, was the study properly controlled? In other words, are we sure that the subjects who did not take guarana supplementation had the same baseline fitness level as those who did? Second, do we have any reason to suspect that taking supplements would have a placebo effect that would lead the study group to overestimate the degree to which their fatigue has been reduced? Third, is it possible that the researchers themselves are biased in favor of discovering the sought-after effect?

We can also weaken the argument by questioning whether the causal relationship can be explained by a third, independent factor. What if people who typically experience lower level of fatigue because of a third, unrelated factor (above-average fitness level, other nutritional supplements, etc.) also tend to take Pump3D? This would imply an alternate cause for the observed effect.

With this in mind, take a look at the following two questions.

Question # 1

Which of the following, if true, would most weaken the argument in the advertisement?

(A) Guarana extract supplements tend to reduce slightly athletes’ endurance and stamina during aerobic exercise.

(B) People who regularly consume guarana extract supplements tend to be professional athletes, who rarely experience fatigue after exercise.

(D) The reduction in fatigue due to the consumption of guarana extract is no greater than the reduction due to other nutritional supplements.

(E) Guarana extract taken in the form of supplements has a different effect on the body than does guarana extract taken in food.

Question # 1: Answer and Analysis

Premise: People who regularly take guarana extract supplements have a significantly lower level of fatigue after anaerobic exercise than people who do not take the supplement.

Premise: Guarana extract is the main ingredient in Pump3D.

Conclusion: Pump3D can greatly reduce athletes’ fatigue after anaerobic exercise.

Answer choice (A) is incorrect, because the scope of the argument is limited to the effects of guarana supplementation on anaerobic exercise alone. The effect on aerobic exercise would only be relevant if the conclusion extended to include other forms of exercise (or exercise in general). Be aware of argument scope, and avoid weakening a more general version of the conclusion than the one presented.
Answer choice (B) is the correct answer choice. Recall that the advertisement’s conclusion is based upon a questionable assumption, since the study only establishes a correlation between lower level of fatigue and guarana supplementation. If the subjects who took guarana extract did not have the same baseline fitness level as those who did, then the study was not properly controlled. This, in turn, opens up the possibility of an alternative interpretation for the observed correlation: rather than arguing that guarana reduces fatigue, it is now possible that some third factor—being a professional athlete, for instance—is causally related both to experiencing lower levels of fatigue (professional athletes rarely do), and to the consumption of guarana extract (professional athletes regularly consume it).
Answer choice (C) may seem attractive, because we know that guarana extract is only one of several ingredients in Pump3D. However, we cannot weaken what we do not know: it is entirely possible that the other ingredients in Pump3D are inactive, or that they only intensify the stimulating effects of guarana.
Answer choice (D) is perhaps the most attractive incorrect answer choice. If the reduction in fatigue due to the consumption of guarana is no greater than the reduction due to other nutritional supplements, this suggests that guarana is not the only (or the best) way to reduce fatigue. Other nutritional supplements work just as well. This does not weaken the conclusion, however, which only argues that a nutritional supplement containing guarana can greatly reduce athletes’ fatigue. The author never claimed that Pump3D would be the best (or the only) way to reduce fatigue. Even if some other supplement is just as good (or better), as long as Pump3D works as advertised the argument still stands.
Answer choice (E) is incorrect, because it plays upon the commonly held belief that supplements are not the “real thing.” Read closely! The study examined subjects who took nutritional supplements containing guarana extract, making it reasonable to draw a conclusion about the effects of a similar supplement, such as Pump3D. Had the study examined the effects of guarana when taken with food, this answer choice would have been a reasonable objection to the conclusion.

Question # 2

Which one of the following is an assumption required by the argument?

(A) The belief that a nutritional supplement would have a certain effect can sometimes produce that effect.

(B) People who regularly take guarana extract do not undertake unusually strenuous exercise regimens that are otherwise conducive to experiencing fatigue.

(C) People who avoid taking nutritional supplements are not more likely to have a healthy, well-balanced diet that combats fatigue.

(D) People who regularly take guarana extract are not significantly more likely than those who do not to consume caffeine, a known stimulant that decreases fatigue.

(E) Consuming guarana extract has few serious side effects.

Question # 2: Answer and Analysis

Knowing the potential flaws in the author’s conclusion is immensely helpful in identifying an assumption upon which that conclusion is based. The answer you select must contain a statement upon which the argument depends, i.e. a statement that is necessary for the conclusion to be true. Typically, if you see a major weakness in an argument where the author relies on a potentially biased experiment to draw a causal conclusion, look for a Defender assumption answer stating that the study was properly controlled. As always, prove the correct answer choice by using the Assumption Negation Technique: if the logical opposite of a given statement weakens the conclusion of the argument, then it must be an assumption upon which the conclusion depends.

Answer choice (A): This answer choice describes a placebo effect, which would weaken the argument, not represent an assumption necessary for the argument to be logically valid. Indeed, if the researchers failed to conduct a “blind experiment” where neither the experiment, nor the control group, were aware of what supplement they were taking, then it is entirely possible that those reporting lower levels of fatigue were influenced by their belief that the nutritional supplement would be effective. Since we are not answering a Weaken question, this answer choice is incorrect.
Answer choice (B): If people who regularly take guarana extract avoid strenuous exercise, no wonder they feel less fatigued than those who do not take guarana. This answer choice also weakens the argument and is incorrect. You can also analyze this answer choice by examining the effect of its logical opposite. What if those who regularly take guarana do exercise a lot, which typically makes one feel tired? This would only strengthen—not weaken—the conclusion that Pump3D reduces fatigue. Why? Because these subjects must have done something right to counteract the fatigue-inducing effects of rigorous exercise (given that they feel less tired than the control group). That “something” could have been Pump3D, suggesting that the supplement might be effective in reducing fatigue.
Answer choice (C): This answer choice states that people who avoid taking nutritional supplements are not more likely than those who do to have a healthy, well-balanced diet that combats fatigue. To examine whether this is an assumption, try negating it: What if those who avoid taking nutritional supplements were more likely than others to have a healthy, well-balanced diet that combats fatigue? In that case, we would expect the control group to be experiencing lower levels of fatigue than the experimental group, which is not the case: in fact, those who consumed guarana were significantly less tired than those who did not. Since we cannot argue with the facts, we are left to conclude that guarana had a positive effect on the subjects who took it, strengthening the conclusion of the argument. The logical opposite of answer choice (C) does not weaken the argument, proving that answer choice (C) is not an assumption upon which that argument depends.
Answer choice (D) is the correct answer choice, because its logical opposite weakens the conclusion. What if people who regularly take guarana extract were more likely than others to consume caffeine, a known stimulant that decreases fatigue? This suggests that their decreased level of fatigue may be due to an alternate cause—caffeine—revealing that the study is based on a potentially biased sample. It is no longer possible to claim with absolute certainty that Pump3D can greatly reduce athletes’ fatigue, because their alertness can be due to the consumption of caffeine instead. Since the logical opposite of answer choice (D) weakens the conclusion of the argument, it is the correct answer to this Assumption question.
Answer choice (E): Whether guarana consumption has any serious side effects is irrelevant to the question of whether it helps reduce athletes’ fatigue. Even if guarana had many side effects, this would only be of concern if the author recommended or endorsed the consumption of guarana extract. The scope of the argument is much narrower, making answer choice (E) incorrect.