1

According to a study in the New England Journal of Medicine, your friendships or "social networks" are more likely than your genes to make you overweight (Jennifer Levitz, "Can Your Friends Make You Fat?" Wall Street Journal, July 26, 2007, D1). If it is true that people who have overweight friends are more likely to be overweight, is that an example of a negative externality? Why? (Hints: Is this relationship a causal one, or do heavier people choose heavier friends?)

2

A number of countries have either banned incandescent light bulbs already or have begun phasing out such lighting in favor of more fuel-efficient compact fluorescent bulbs. These restrictions are intended to promote energy conservation and therefore to reduce greenhouse gas emissions and global warming. What alternative approaches could a government use to achieve the same goals? What are the advantages and disadvantages of a ban relative to the alternatives?