An investigation into the relationship between team size and productivity by Alan Ingham and three colleagues in the 1970s found people worked less hard in a group. This problem is referred to as social loafing—where productivity in groups goes down because each individual feels less responsible for the output. The research indicates people prefer teams of four or five members.  If reducing the size of your team is not an option, consider dividing tasks into smaller bits for every member of the team to be responsible for. Perhaps weaker team members could be made disproportionately responsible for their portion of the workload. Another option is to open performance feedback to the rest of the group. 

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