In 1954, Gordon Allport suggested that by promoting contact between groups, prejudice can be reduced. Further, he suggested four optimal conditions for contact: equal status between the groups in the situation; common goals; intergroup cooperation; and the support of authorities, law, or customs. Since then, over 500 studies have been done on prejudice reduction under variations of the contact hypothesis, and a meta-analytic review suggests overall support for its efficacy. In some cases, even without the four optimal conditions outlined by Allport, prejudice between groups can be reduced.