Logical Reasoning

PT129 · S3 · Q10 Columnist: The failure of bicyclists

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Columnist: The failure of bicyclists to obey traffic regulations is a causal factor in more than one quarter of the traffic accidents involving bicycles.

Conclusion

Bicyclists are least partially responsible for over half of accidents involving bikes.

Evidence

More than 1/4 of accidents involving bikes involve a biker failing to obey a traffic rule. More than 1/4 of accidents involving bikes involve a biker with inadequate safety equipment.

Evaluation

The intended logic is that if more than 25% of accidents come from breaking rules and more than 25% come from inadequate equipment, then more than 50% of accidents come from "breaking rules or inadequate equipment" (i.e. bikers who are at least partially responsible).

Quick analogy: 50% of Americans follow the NBA. 50% of Americans follow the NFL. Thus every American is either an NBA fan or an NFL fan.

The problem there is that those 50% groups can be highly overlapping. Let's go overboard with stereotyping to make the math easy to see. Suppose that all males like sports, so they follow the NBA and the NFL. Suppose that all females don't like sports so they don't follow the NBA or the NFL. In this case, it would be true to say that 50% of the US follows the NBA, and 50% follows the NFL, but it would only be 50% of Americans that are an NBA fan or NFL fan.

Similarly, in this argument with the bicyclists, there could be responsible bikers who always follow traffic rules and have adequate safety equipment. They aren't involved in either type of accident we heard about. Then there are irresponsible bikers (like me), who break traffic rules and have inadequate safety equipment. When we get into accidents, it's possible that our rule-breaking and our shoddy safety equipment are both causal factors. So even if we're only involved in 27% of all accidents involving bikes, the premises would still be true (more than 25% of accidents involved rule breaking ... more than 25% involved bad equipment) but the conclusion would not.

Goal

Look for something like, .

10.

The columnist's reasoning is flawed in that it

  1. presumes, without providing justification, that

    Bad Conclusion Match

    The conclusion is only saying that bikers are at least partially responsible, so there's still room in the author's words for believing that she would also consider motorists a factor in more than half of the accidents. More than one cause can be a factor. More than one entity can be a culpable party.

    6% picked this

  2. improperly infers the presence of

    Bad Premise Match

    Does the conclusion claim some causal connection? Yes, it says bikers are at least partially "responsible". Is the evidence a correlation? No, it's two different statistics that actually involve causality themselves. A correlation would sound like "bikers who disobey traffic regulations are more likely than those who don't to be involved in an accident". They suggest causality but they don't outright say it or imply it. Meanwhile the author's evidence says that "disobeying traffic regulations is a causal factor in more than 25% of accidents".

    22% picked this

  3. Correct

    fails to consider the possibility

    Why this is right

    Can we object to the author's argument by pointing out that accidents can have more than one causal factor? Yes, we can make the argument that 27 out of 100 accidents had both rule-breaking and bad equipment as two of their causal factors. That sort of scenario shows that the bikers were at least partially responsible in 27% of cases, not in over 50% of cases as the author has concluded.

    Skill tested: Flaw · how this choice captures the argument's function is the move to repeat next time.

    72% picked this

  4. fails to provide the source

    Not a Flaw

    When we're evaluating flawed reasoning, we're saying, "EVEN IF we accept your background facts, you still haven't proven your conclusion." This answer is acting like we shouldn't accept the background facts. If the author had provided the source of the figures, would that have convinced us whether those figures were accurate or not? No, we would still need to know more about the source and about these figures in order to verify their accuracy. Flaw questions aren't about fact-checking any data presented in the premises. We grant the author the truth of that data but still find a way to argue that their conclusion isn't something we can confidently infer.

    0% picked this

  5. fails to consider that the

    Out of Scope: "severity"

    We debate the truth value of the Conclusion. The conclusion is a statistical claim about whether bikers are a causal factor in more than 50% of accidents. Our objections can only be relevant if they help us decide whether bikers are a causal factor in more than 50% or less than 50% of accidents. The relative "severity" of an accident doesn't matter. The stat we're evaluating is simply, "whether or not the biker was at least partially responsible" . It doesn't even matter how responsible they were. If it was more than zero, then it counts towards the author's conclusion.

    0% picked this

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