Passage Summary: Most people who suffer from extreme insomnia drink a lot of coffee. Because Tom drinks a lot of coffee, the author assumes he is probably one of those insomniacs.

Conclusion: Tom is likely an extreme insomniac.

Reasoning: Ninety percent of extreme insomniacs drink a lot of coffee, and Tom is a heavy coffee drinker.

Analysis: This argument commits a classic error in conditional or probabilistic reasoning. It confuses the percentage of a specific subgroup (insomniacs) who have a trait (drinking coffee) with the likelihood that anyone with that trait belongs to the subgroup. There could be millions of people who drink coffee but sleep perfectly well, making the actual number of coffee-drinking insomniacs a tiny fraction of the total coffee-drinking population. Look for an answer that identifies this confusion between the characteristics of a small group and the characteristics of the general population.