Some factors which influence the forming of relationships include the theory of proximity, which refers to how close we are to each other. Back et al., (2008, in Hogg and Vaughn, 2007) found that after randomly assigning students to particular seats, their initial ratings were more positive the closer they were seated. One year later, they had formed strong friendships with those who were sat next to them, so supporting this theory. The theory of familiarity, originally suggested by Zajonc (1968, in Kelley, 1992), means the more often you encounter someone, the more chances of liking them. Moreland and Beach (1992, in Knud S. Larsen, 2008) had a group of female stooges enter a university class a number of times, having no interaction with any of the students. The results showed the more times a stooge entered the classroom, the more attractive the students rated them, seeming familiar leads to liking. Both proximity and familiarity are referred to as situational factors, in that the situation we find ourselves in could influence results.
There are also personal factors involved, such as similarity and attractiveness. Byrne and Nelson (1965, in Kelley, 1992) found, after providing participants with information on fictitious people and having manipulated similarities, that the more similarities they had, the more participant liked them. Singh and Ho (2000, in Hogg and Vaughn, 2007) found participants were repulsed by people who had very different attitudes to themselves. These results show good reliability for the theory of similarity. Attitudes are simply likes and dislikes, therefore, people with similar attitudes are reinforcing so it is natural to want to form a relationship. However, this study is artificial and, therefore, lacks ecological validity. It is just as common for relationships to occur when people get to know each other through work or socially, but have different levels of similarity or attractiveness.