(a)

Author (year)	Duration of illness (in years)	Comment
Abrams and Taylor (1974) [13]	10.86	—
Abrams et al. (1979) [14]	11.7	—
Nurnberger et al. (1979) [18]	—	29% of patients converted to BD over follow-up of 4 months.
Perris (1982) [10]	—	Polarity changes from mania to depression after 3rd episode and rare after 8th episode.
Srinivasan et al. (1982) [19]	5	—
Khanna et al. (1992) [20]	9.5	—
Avasthi et al. (1996) [21]	7	—
Aghanwa (2001) [22]	16.6	—
Yazici et al. (2002) [23]	12	—