How do I grade collaborative work?

I'm not a specialist

Decide on the main elements, and creat a rubric.

Collaboration is working with each other to do a task and to achieve shared goals.It is a recursiveprocess where two or more people or organizations work together to realize shared goals, (this is more than the intersection of common goals seen in co-operative ventures, but a deep, collective, determination to reach an identical objective— for example, an endeavor that is creative in natureby sharing knowledge, learning and building consensus. Most collaboration requires leadership, although the form of leadership can be social within a decentralized and egalitarian group. In particular, teams that work collaboratively can obtain greater resources, recognition and reward when facing competition for finite resources.Collaboration is also present in opposing goals exhibiting the notion of adversarial collaboration, though this is not a common case for using the word.

Grade each of them

Shared Group Grade Method can be used to grade collaborative work . 

The group perfoms and all group members receive the same grade, regardless of individual contribution.

The decision to grade group work depends on the nature and desired outcomes of the assignment. Some faculty who grade collaborative work award each student in the group the same grade, a strategy that may work best when the stakes are relatively low. Others award grades both for individual and collective effort. One way to determine group grades (either in part or as a whole) is to ask students to evaluate one another's work on a standard form.

I can say that colloborative work is a key of success for any reseach. In colloborative work you have chance to select many super specialized experts who can collectivley make fruitful results. (Proverb: Join all fingers of a hand to make a punch, individual fingers cannot make a punch).

Thanking you

Shared Group Grade

The group submits one product and all group members receive the same grade, regardless of individual contribution.

Advantages:

encourages group work - groups sink or swim together

decreases likelihood of plagiarism (more likely with individual products from group work)

Disadvantages:

relatively straightforward method

individual contributions are not necessarily reflected in the marks

stronger students may be unfairly disadvantaged by weaker ones and vice versa