Critically

People put in less effort when their own contribution can't be seen

Social loafing is the drop in individual effort that happens when people work as a group. Research has found that it shrinks when each person's output can be identified. It isn't limited to physical tasks. One study found loafing on a thought-provoking task where each person could make a unique contribution. On Critically, every note and citation carries its author's name, so each person's share of a shared notebook is visible.

Some duplication is deliberate

Dividing the work doesn't mean every item is read only once. Cochrane recommends that at least two people extract key data independently. It cites a study in which independent double extraction produced fewer errors than one person extracting and a second checking. Decide in advance which items get read twice, starting with the claims the notebook depends on most. A 2017 methods review notes that the evidence behind these standards is weak, even though extraction errors are common.