Various institutions and organizations have given widely varying estimates about how many Muslims live in the U.S. Tom W. Smith, author of "Estimating the Muslim Population in the United States," said that of twenty estimates he reviewed during a five-year period until 2001, none was "based on a scientifically-sound or explicit methodology. All can probably be characterized as guesses or assertions. Nine came from Muslim organizations such as the Islamic Society of North America, the Muslim Student Association, the Council on American-Islamic Relations, the American Muslim Council, and the Harvard Islamic Society or unspecified "Muslim sources."