相关关系：AB正相关或者负相关
因果关系：A→B
相关和因果是GMAT逻辑部分考察的一大要点。我们知道相关关系不等同于因果关系：因果关系必定是相关关系，而相关关系不一定是因果关系。
统计数据表明，2010-2019年每年的冰淇淋销量和游泳池淹死的人数成正相关，即A（吃冰淇淋）和B（在游泳池淹死）相关，但显然AB之间不存在因果关系，吃冰淇淋不会导致在游泳池淹死，在游泳池淹死也不会导致人们吃冰淇淋。AB之间的相关关系是因为一个混淆变量（天气炎热程度）的存在。
某公众号发表了一篇阅读量100000+的文章，攻击某知名连锁品牌“啃的鸡”：《揭露！中国人必转！洋快餐是如何残害祖国花朵的！》，证据是一个抽样调查（全国十大省会城市10000名初中生）表明，每个月吃“啃的鸡”次数和初中生的肥胖程度正相关。统计数据显示的是相关关系：A（吃啃的鸡）和B（肥胖）相关，文章结论却直接变成了因果关系：吃啃的鸡导致肥胖。“啃的鸡”欲反驳该文章，可以从两个不同角度削弱：1，这些肥胖的学生对自己每日摄入的卡路里缺乏管理，摄入量大于消耗量才导致发胖，吃啃的鸡并不会2，不是吃啃的鸡发胖，而是胖子喜欢吃东西，不止吃啃的鸡还吃麦当劳德克士汉堡王......
通过“啃的鸡”的例子，我们可以抽象出解决GMAT逻辑相关和因果题目的如下思路。
削弱题，欲反驳或削弱A→B，手段有二：1，引入他因，2，因果倒置。
推及假设题和加强题，欲支持或加强A→B，手段有二：1，排除他因，2，否定因果倒置。
假设题示例1 OG2018-Q635
In Wareland last year, 16 percent of licensed drivers under 21 and 11 percent of drivers ages 21–24 were in serious accidents. By contrast, only 3 percent of licensed drivers 65 and older were involved in serious accidents. These figures clearly show that the greater experience and developed habits of caution possessed by drivers in the 65-and-older group make them far safer behind the wheel than the younger drivers are.
Which of the following is an assumption on which the argument depends?
A. Drivers 65 and older do not, on average, drive very many fewer miles per year than drivers 24 and younger.
B. Drivers 65 and older do not constitute a significantly larger percentage of licensed drivers in Wareland than drivers ages 18– 24 do.
C. Drivers 65 and older are less likely than are drivers 24 and younger to drive during weather conditions that greatly increase the risk of accidents.
D. The difference between the accident rate of drivers under 21 and of those ages 21–24 is attributable to the greater driving experience of those in the older group.
E. There is no age bracket for which the accident rate is lower than it is for licensed drivers 65 and older.
解析：排除他因
首先简化题干：前提是统计数据表明司机年龄A和事故率B成负相关，年轻司机事故率高，年长司机事故率低。结论是年长司机（随年龄而来的）丰富的经验和长期形成的开车谨慎的习惯A导致他们事故率低B。假设题需要支持因果关系，使逻辑链完整，手段2否定因果倒置（不是事故率低导致经验丰富开车谨慎）在这道题行不通，手段1排除他因（不是其他原因导致事故率低），对应A选项（不是因为开得少事故率才低）。当然，A选项取非后就成了引入他因，可用来削弱原文结论。
假设题示例2
A researcher discovered that people who have low levels of immune-system activity tend to score much lower on tests of mental health than do people with normal or high immune-system activity. The researcher concluded from this experiment that the immune system protects against mental illness as well as against physical disease.
The researcher's conclusion depends on which of the following assumptions?
A. High immune-system activity protects against mental illness better than normal immune-system activity does.
B. Mental illness is similar to physical disease in its effects on body system.
C. People with high immune-system activity cannot develop mental illness.
D. Mental illness does not cause people's immune-system activity to decrease.
E. Psychological treatment of mental illness is not as is medical treatment.
解析：否定因果倒置
首先简化题干：前提是统计数据表明免疫系统活动水平A和精神健康程度B成正相关，结论是免疫系统活动水平高A会导致精神健康程度高B。假设题需要支持因果关系，使逻辑链完整，手段1排除他因（不是其他原因导致精神健康程度高B）在这道题行不通，因为精神健康可能由多个原因导致，手段2否定因果倒置（不是精神健康程度B影响免疫系统活动水平A）对应D选项。
削弱题示例1 OG2018-Q549
Editorial: The roof of Northtown’s municipal equipment storage building collapsed under the weight of last week’s heavy snowfall. The building was constructed recently and met local building safety codes in every particular, except that the nails used for attaching roof supports to the building’s columns were of a smaller size than the codes specify for this purpose. Clearly, this collapse exemplifies how even a single, apparently insignificant departure from safety standards can have severe consequences.
Which of the following, if true, most seriously weakens the editorial’s argument?
A. The only other buildings to suffer roof collapses from the weight of the snowfall were older buildings constructed according to less exacting standards than those in the codes.
B. The amount of snow that accumulated on the roof of the equipment storage building was greater than the predicted maximum that was used in drawing up the safety codes.
C. Because the equipment storage building was not intended for human occupation, some safety code provisions that would have applied to an office building did not apply to it.
D. The municipality of Northtown itself has the responsibility for ensuring that buildings constructed within its boundaries meet the provisions of the building safety codes.
E. Because the equipment storage building was used for storing snow removal equipment, the building was almost completely empty when the roof collapsed.
解析：引入他因
首先简化题干：前提是钉子不符合建房标准A，下大雪后房屋倒塌B。结论是A→B。欲削弱原文，可引入他因C（雪太大），C→B，对应B选项。
削弱题示例2 OG2018-Q574
People who do regular volunteer work tend to live longer, on average, than people who do not. It has been found that “doing good,” a category that certainly includes volunteer work, releases endorphins, the brain’s natural opiates, which induce in people a feeling of well being. Clearly, there is a connection: Regular releases of endorphins must in some way help to extend people’s lives.
Which of the following, if true, most seriously undermines the force of the evidence given as support for the hypothesis that endorphins promote longevity?
A. People who do regular volunteer work are only somewhat more likely than others to characterize the work they do for a living as “doing good.”
B. Although extremely high levels of endorphins could be harmful to health, such levels are never reached as a result of the natural release of endorphins.
C. There are many people who have done some volunteer work but who do not do such work regularly.
D. People tend not to become involved in regular volunteer work unless they are healthy and energetic to begin with.
E. Releases of endorphins are responsible for the sense of well
being experienced by many long distance runners while running.
解析：因果倒置
首先简化题干：前提是A（做志愿工作）和B（寿命长）相关，做志愿工作A可导致人大脑分泌可增强幸福感的物质C（A→C）。结论是C→B，根据前提A→C，结论可替换成A→B。欲反驳因果关系，因果倒置（寿命长的人才能做志愿工作，而非做志愿工作使人寿命长）对应D选项。
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