Non-rich people tend to spend 100 percent of their income, or close to it. Rich people don’t. They spend, say, 50 percent of their income and save the rest. This difference is called the “marginal propensity to consume,” and it seems like it might be a problem if income inequality is rising. The problem is that as rich people get a larger share of total income, total consumption goes down. Here’s an example:
The question, of course, is how big the MPC effect is. Several years ago I investigated this and concluded that it really wasn’t very big. It seems like it should be, but it just wasn’t.
Today, however, Larry Summers directs our attention to a new IMF paper that suggests MPC actually does have a big impact. The authors look at two effects. First, as middle-income families fall into lower income groups, they spend less. Second, as a larger share of income goes to the rich, average MPC goes down. Both of these effects reduce total consumption, which in turn acts as a drag on the economy. Here’s the relevant chart: (Source)