Table 2.

Definitions of age at onset of bipolar disorder.

Study	Design	Sample (bipolar patients)a	Very early age at onset (in years)	Early age at onset (in years)	Intermediate age at onset (in years)	Late age at onset (in years)
Schürhoff et al., 2000b [10]	Cross-sectional	210	—	<18	—	>40
Schulze et al., 2002b [17]	Cross-sectional	169	—	≤20	—	≥35
Post et al., 2003b [18]	Cross-sectional	320 (202 female; 118 male)	—	≤18	—	>18
Bellivier et al., 2003c [19]	Cross-sectional	368	—	Median age: 17.4	Median age: 25.1	Median age: 40.4
Perlis et al., 2004c [20]	Cross-sectional	1,000	<13	13–18	—	>18
Lin et al., 2006c [21]	Cross-sectional	1,856 (211 probands)	—	≤21 Mean age: 16.6	22–28 Mean age: 26	>28 Mean age: 34.7
Benazzi and Akiskal, 2008 [22]	Cross-sectional	560d	—	<21	—	>21
Hamshere et al., 2009c [23]	Cross-sectional	1,369	—	Limit: <22 mean age: 18.7 ± 3.7	Limit: 25–37 mean age: 28.3 ± 5.5	Limit: >40 mean age: 43.3 ± 9.1
Etain et al., 2012c [3]	Cross-sectional	652	—	<21	—	≥21

(based on Hamshere et al. 2009 [23]).

^aSome studies do not classify the patients whose diagnosis was included.

^bAge of both bipolar disorder (BD) type I and BD type II.

^cAge of BD type I.

^d336 BD type II and 224 unipolar major depressive disorder.