The American Association of Museums (AAM) has re-accredited 42 institutions and added three new museums to its portfolio, which consists of 774 out of the nation's 20,000 museums.

The AAM accreditation programme is the sector's primary vehicle for quality assurance, self-regulation and public accountability.

A spokesperson for the AAM said: "The characteristics of an accreditable museum establish outcomes towards which all museums should strive and achieve in ways appropriate to their resources.

"To best serve their communities it is essential that museums be committed to institutional improvements, maintaining standards in collections stewardship, governance, institutional planning, ethics, education and risk management."

The three new museums added are the Mary and Leigh Block Museum of Art in Evanston, Illinois, the Museum of Northern Arizona, Arizona, and Washington Pavillion of Arts and Sciences in Sioux Falls, South Dakota.

Ford Bell, AAM president, said: "As accredited institutions, these 45 museums have achieved the highest standard of service to the public. The communities that these museums serve can take great pride in having an invaluable public asset in their midst."

To earn accreditation museums must compile a report consisting of a a year-long self-study and the results of a site visit. The average processing time is three years.