MPO and major depressive disorder: As found in previous studies, polarity at onset was associated with the polarity of subsequent depressive episodes (Carvalho et al., 2014; Colom et al., 2006; Perugi et al., 2000; Tundo et al., 2015): DPO patients had more depressive episodes than MPO patients, while there were no differences regarding the total number of manic episodes.