The United States Federal Reserve published data on three monetary aggregates until 2006, when it ceased publication of M3 data and only published data on M1 and M2. M1 consists of money commonly used for payment, basically currency in circulation and checking account balances; and M2 includes M1 plus balances that generally are similar to transaction accounts and that, for the most part, can be converted fairly readily to M1 with little or no loss of principal. The M2 measure is thought to be held primarily by households. Prior to its discontinuation, M3 comprised M2 plus certain accounts that are held by entities other than individuals and are issued by banks and thrift institutions to augment M2-type balances in meeting credit demands, as well as balances in money market mutual funds held by institutional investors. The aggregates have had different roles in monetary policy as their reliability as guides has changed. The principal components are: