Research on collaboration in social networks is largely restricted by a lack of longitudinal data. Approximations of collaborative intensity nec-essarily rely on the width of collaboration, such as the number of papers two scientists have coauthorcd. In contrast, wc discuss precise measures of collaborative intensity with respect to not only the width but also the depth of collaboration. Based on empirical data of four social networks, wc compare a widely-used approximation with our own measures of collaborative intensity. Wc find that the quality of the approximation varies with the type of social networks.