If groups with a negative outlook were brought together, it would lead to increases of negative attitudes rather than positive. Allport situated his formulation of the contact hypothesis in broader discussion of racial diversity—a precursor to interracial proximity and contact. While diversity more generally might foment conflict and prejudice, Allport suggested that contact, under four particular conditions, would facilitate intergroup understanding and consequently reduce prejudice. In the years prior to Allport’s framing of intergroup contact theory, social scientists had already begun discussing the conditions of intergroup contact that would produce intergroup anxiety, prejudice, or other “detrimental psychological effects”. Wilner, Walkley, & Cook, two years prior to "The Nature of Prejudice", studied segregation and integration in housing projects, and also suggested four conditions under which intergroup attitudes would change for the better. Under the assumption that prejudice arises from racial segregation, they suggested that it would diminish when members occupy “the same or equivalent roles in the situation,” share background characteristics like education, age, gender or socioeconomic status, perceive common interests or goals, and when the “social climate […] is not unfavorable to interracial association.” Concurrently, Carolyn Sherif and Muzafer Sherif developed their Robbers Cave experiment, an illustration of realistic conflict theory. The Sherifs highlighted the importance of superordinate goals and equal status between groups, but notably, did not weigh in alongside other social scientists in their amicus brief for Brown v. Board of Education. In Allport's own words,   In other words, four conditions under which intergroup contact will reduce prejudice are:   Additionally, Allport specified that within intergroup cooperation, personal interaction, involving informal, personal interaction between group members would scaffold learning about each other and the formation of cross-group friendships. Yet, without these conditions, casual, or superficial, contact would cause people to resort to stereotypes. The largest meta-analysis of the contact literature suggested that the conditions are facilitating but not essential. However, more recent meta-analysis highlights that many configurations of the conditions have not yet been experimentally tested. A number of psychological processes have been hypothesised to explain how and why intergroup contact is able to reduce prejudice and improve intergroup relations. Firstly, Allport (1954) argued that intergroup contact facilitates learning about the outgroup, and this new outgroup knowledge leads to prejudice reduction. Secondly, intergroup contact is believed to reduce the fear and anxiety people have when interacting with the outgroup, which in turn reduces their negative evaluations of the outgroup.