Study	Reason for exclusion
Clini 1998	The assignment of the participants to the 2 groups was not randomised
Diaz 1999	Participants received NIPPV for 3 hours a day. We believe that NIPPV should be applied during the night for at least 5 hours per night
Kamei 1999	The assignment of the participants to either NIPPV or long‐term oxygen therapy groups was not randomised
Lin 1996	Participants received NIPPV for only 2 weeks. It is difficult to start NIPPV in people with COPD, therefore, it is necessary to determine the effects after a longer period so the participants can adjust to the ventilator
Renston 1994	People received NIPPV for 2 hours a day for 5 day. We believe that NIPPV should be applied during the night for at least 5 hours per night.

COPD: chronic obstructive pulmonary disease; NIPPV: non‐invasive positive pressure ventilation.