QUESTION TEXT: Records from 1850 to 1900 show that…
QUESTION TYPE: Method of Reasoning
CONCLUSION: A baby’s health depends on how much food the mother gets while she is pregnant.
REASONING: There was a correlation between babies’ birth weights and the success of crops the year before.
ANALYSIS: This argument has two flaws. First, it uses evidence from a correlation to prove causation. This never works. Second, it switches terms inappropriately. Stop – before reading this explanation, look at the reasoning and conclusion again – try to spot the shifts in terms.
Did you find it? The argument switches from birth weight to health and from crop success to food access. These shifts aren’t warranted. First, birth weights. A higher birth weight doesn’t necessarily mean a baby is healthier. The argument should have made this explicit.
Second, crop success. Maybe crop success doesn’t lead to more food for mothers. This could be a region of farmers. When crops succeed, the mothers are richer, less stressed, etc. But perhaps they normally have enough food either way.
- CORRECT. See the explanation above. The “claimed correlation” is between birth weights and crops. The causal relation is between health and food access.
- An example of this would be “….therefore, babies’ birth weights are only affected by crop success”. The argument didn’t say anything like that.
- An example of this would be “….since there used to be a correlation between crops and birth weights, there is still such a correlation.”
- An example of this would be “….because birth weights and crop records are linked, there must be a common cause. Maybe weather explains both crop success and heavier birth weights.”
- There are two reasons this is wrong. First, the argument didn’t explain any causal relations. Second, there aren’t two causal relations! The relation between crop success and birth weights is just a correlation.
Free Logical Reasoning lesson
Get a free sample of the Logical Reasoning Mastery Seminar. Learn tips for solving LR questions