Self-study
In 2005, an environmental group conducted a study measuring the levels of toxic chemicals in the bodies of eleven volunteers. Scientifically valid inferences could not be drawn from the study because of the small sample size, but the results were interesting nonetheless. Among the subjects tested, younger subjects showed much lower levels of PCBs—toxic chemicals that were banned in the 1970s. This proves that the regulation banning PCBs was effective in reducing human exposure to those chemicals.
22.
The reasoning in the argument is most vulnerable to criticism on the grounds that the argument
a
takes an inconsistent stance regarding the status of the inferences that can be drawn from the study
This captures exactly what the author does. She first declares that no valid inferences can be drawn from the study, then turns around and draws an inference and calls it proven. That's two opposing positions on whether the study can support inferences.
b
overlooks the possibility that two or more chemicals produce the same effects
The argument doesn't involve the effects of chemicals. It involves the levels of one specific chemical (PCBs) in people's bodies. Whether some other chemical produces the same effects as PCBs has no bearing on whether the ban reduced PCB exposure.
c
concludes that a generalization has been proven true merely on the grounds that it has not been proven false
The author isn't arguing from a lack of evidence. She's offering evidence (the study), even after admitting that evidence is too thin. The pattern (C) describes is "X is true because nobody has disproven it." The author isn't relying on the absence of disproof; she's relying on the presence of weak proof. Those are different problems.
d
takes something to be the cause of a reduction when it could have been an effect of that reduction
This describes reverse causation: treating X as having caused Y when it was actually Y that caused X. For this to match, we'd need a story where reduced PCB levels caused the regulation banning PCBs. But that runs the timeline backward. The ban was passed in the 1970s; the data showing reduced levels came in 2005. And bans aren't caused by the chemical levels they target. They target those levels in order to change them.
Students get drawn to (D) because the conclusion is causal ("the ban reduced exposure") and reverse causation is a famous LSAT flaw. The reflex of "this is causal, so check for reverse causation" kicks in. But not every causal argument has a reverse causation problem. Here, the direction of cause and effect isn't in dispute.
e
does not consider the possibility that PCBs have detrimental effects on human health several years after exposure
The argument doesn't address the health effects of PCBs at any point. It's about exposure levels, that is, how much PCB ends up in people's bodies. Whether PCBs cause health problems years after exposure is a separate issue and wouldn't affect the conclusion that the ban reduced exposure.