That pace is five times the expected growth rate for overall household assets.

"The percent of household assets in equities is at historically high levels," he said.

Most of the decline in household assets can be attributed to skidding stock prices.

Even the Fed's key person on the issue says that these investment products should be included in any study of household assets.

At the end of 2011, funds accounted for 23% of household financial assets.

Japanese invest only about 2.6 percent of their household assets in mutual funds.

Another study found that the richest 2% own more than half of global household assets.

Instead, it tracks most household assets - real estate, bank accounts, securities and so on - in its regular reports.

By 2004, real estate was 32 percent of household assets, up from 26 percent in 2000.

Personal debts are 12% of household assets, which is a relatively low ratio in developed economies.