In 1962 Kerckoff and Davis presented another form of relationship formation theory known as the filter model

In 1962 Kerckoff and Davis presented another form of relationship formation theory known as the filter model. They believed that we have three filters that are important at different times before we can enter a relationship. We start with a field of availables, those who are free for relationships and gradually narrow them down using different stages to a field of desirables, and those who we would consider as potential partners. The first filter is the social and demographic variables where we tend to pick people with similar educational and economic background to us. The second filter is the similarity of attitudes and values, where people with different values, attitudes and interests to us are filtered out. The third stage is the complementarity of emotional needs where we decide how well between the two people they fit together as a couple.
Kerckoff and Davis (1962) then tested their model in a longitudinal study using student couples that had been together for more or less than 18 months. They completed several questionnaires over 7 months which reported on attitude similarity and personality traits with their partner. They found that attitude similarity was the most important factor up to about 18 months into a relationship, after this time psychological compatibility and the ability to meet each other’s needs became important, supporting the idea of the filter model.
The filter model is a useful way to think about factors that are influential in relationship development and when they might come into play. It also emphasises the importance of demographic factors and similarity of attitudes and values as filters in development of relationships, evidence shows this continues in relationship survival. However the division of relationships into stages fails to capture their fluid and dynamic nature. Real life relationships flow seamlessly. Some may develop faster and others slower than the filter model suggests.