Conjunctive tasks are a part of Steiner's taxonomy of group tasks. They are often studied when dealing with process losses in groups. Process loss is observed in groups when there is a reduction in their performance effectiveness or efficiency. This could be due to a variety of interpersonal processes, which may be caused by either motivation loss or coordination loss. Conjunctive tasks fall into the latter category of coordination problems in groups.
The Most Inferior Group Member (IGM)
Conjunctive tasks are tasks where all group members must contribute to the end product in order for it to be completed. On most tasks, a group's performance is the result of a combination of everyone's effort; however, with conjunctive tasks, the group's overall performance depends on the most inferior group member (IGM). Colloquially this person is often termed the "weakest link." Conjunctive tasks are not complete until the entire group has completed their portion of the job. Consequently, the speed and quality of the work is dependent on the least skilled member of the group. In this way, this group member is like the rate determining step. It would be to the benefit of the group to assign the easiest subtask to such a member. Conversely, if they are matched with the most difficult and complex subtasks, the group's overall performance will further suffer.
The Köhler Effect
No one wants to be the weakest link of any group. As a result, weaker individuals in the group respond to this by expending more effort than they would had they been working alone. This is known as the Köhler effect, where performance gains are seen in weaker individuals who are striving to keep up with the accomplishments of other group members. Individuals who perform inferior work compared to someone else show improvement relative to those deprived of this comparison. Moreover, this gain is even more marked when they are part of a group working on a conjunctive task. A recent meta-analysis of related studies has confirmed the presence of the Köhler effect, and has noted that it seems to be stronger in women than men 
- Steiner, I.D. (1972). Group Processes and Productivity. Academic Press.
- Köhler, 1926
- Weber & Hertel, 2007