Discussion
In a detailed study of annual crow births in India, it was found that there was relatively no growth during the period 2002 to 2004 and a sudden spike from 2004 to 2005. In another unrelated study, it was found that the revenue from cracker sales in India which remained fairly flat from 2002 to 2004, saw a sudden spike in 2005 before declining again in 2006. The solid line in the graph below refers to annual sale of crackers and the dashed line refers to the annual crow births in India. Choose the most appropriate inference from the above data.
[The graph, with years 2001 to 2007 on the horizontal axis, shows the two curves moving together: both rise from 2001, stay nearly flat from 2002 to 2004, climb to a peak in 2005 and fall in 2006, the dashed curve lying just above the solid one.]
Answer: A
The appropriate inference is there is a strong correlation between crow birth and cracker sales.
The two series move together year by year: flat from 2002 to 2004, a spike in 2005 and a fall afterwards. That is a strong correlation. But the question itself says the studies are unrelated, and nothing in the data shows a mechanism linking crows and crackers.
So the data support only the statement of correlation. Saying crackers increase crow births, or that crow births cause cracker sales, claims causation, and predicting that a fall in cracker sales will reduce crow births assumes the same causal link. Correlation alone does not establish any of these.
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