Several activities related to human-computer interaction (HCI) design are described in literature. However, it is not clear whether each HCI activity is equally important. We propose a multi-disciplinary framework to organise HCI work in phases, activities, methods, roles, and deliverables. Using regression analyses on data from 50 industry projects, we derive weights for the HCI activities in proportion to the impact they make on usability, and compare these with the recommended and assigned weights. The scores of 4 HCI activities (user studies, user interface design, usability evaluation of the user interface, and development support) have the most impact on the Usability Goals Achievement Metric (UGAM) and account for 58% of variation in it.