Assume a team of 10 members including the team leader. If one member does not contribute, as desired, what would be its negative impact towards the deadline of completing the task ? Answer in % is advisable.
It depends on the nature of the task and the nature of other team members' contributions. In extreme cases, an incompetent team member's lack of contribution can actually improve the quality of a team's work.
Donelson Forsyth's Group Dynamics has a great chapter on teams if you would like an overview of the multitude of variables that influence team effectiveness.