Before revision:  However, pre-pandemic experimental studies have produced mixed results regarding their effectiveness against respiratory viruses  , leading to confusion over whether masks protect the wearer, or only those with whom the wearer interacts .
After revision:  However, pre-pandemic experimental studies have produced mixed results regarding their effectiveness against respiratory viruses . The implications of the studies' recognized limitations have not been quantitatively and statistically analyzed , leading to confusion over whether masks protect the wearer, or only those with whom the wearer interacts .