Research on the well-being of Americans indicates that the

A) vast majority of Americans currently declare themselves to be very happy.
B) personal happiness of Americans has been increasing during the last half-century.
C) buying power of Americans has been decreasing during the last half-century.
D) increase in the buying power of Americans during the last half-century has provided no apparent boost to Americans' personal happiness.

Research suggests that while there has been a significant increase in the buying power of Americans over the last half-century, this has not translated into a noticeable increase in personal happiness. Therefore, option D is the correct answer as it states that the increase in buying power has not boosted personal happiness. Option A is incorrect as the majority of Americans do not actually declare themselves to be very happy. Option B is also incorrect as personal happiness has not been increasing. Option C is incorrect as it states that buying power has been decreasing, whereas research suggests the opposite.