Even though a lot of projects fail due to social issues or personality conflicts, only a small number of empirical studies have been conducted to quantitatively assess the impact of individual personality attributes on the software being developed and the team developing that software. The goal of this paper is to quantify the abstract notion of team homogeneity and to measure its impact on software quality and team productivity. A metric called team homogeneity index (THI) is proposed for this purpose. The six-step process of calculating the THI of a software development team is described and illustrated with the help of an example. Finally, the utility of THI is assessed by conducting a controlled experiment in two different phases of the software development life cycle (SDLC), i.e., implementation and testing. The results reveal that, during the implementation phase, teams with greater THI values were noticeably more productive and produced better quality code. Similarly, during the testing phase, teams with higher values of THI tested more features and wrote better quality test cases. Therefore, the evidence obtained so far suggests that the newly proposed metric, THI, appears to be useful in predicting the quality of software and the productivity of software development teams. Future work includes determining the weights of the five traits using input from the software industry and replication of this empirical study on different phases of SDLC with software practitioners to validate our findings.