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Table 2 Comparison of clinical correlates between early and late onset bipolar disorder type 1 and type 2 patients

From: Clinical correlates of age at onset distribution in bipolar disorder: a comparison between diagnostic subgroups

Clinical variable

Bipolar disorder type 1 (N = 224)

χ 2 or t

P

Early onset (N = 169)

Late onset (N = 55)

Female (%)

73 (43.2)

26 (47.3)

0.3

0.6

Age at interview, mean (SD)

45.3 (13.5)

53.1 (8.8)

4.0

<0.0001

Presence of family history of any psychiatric disorder (%)a

99 (58.9)

37 (67.3)

1.2

0.3

Presence of family history of mood disorder (%)b

85 (52.5)

34 (68.0)

3.7

0.05

Presence of family history of bipolar disorder (%)c

31 (18.5)

13 (23.6)

0.7

0.4

Number of manic/hypomanic episodes, mean (SD)d

4.4 (5.1)

3.6 (3.2)

−1.1

0.3

Number of depressive episodes, mean (SD)e

5.5 (4.7)

4.8 (4.4)

−0.9

0.3

Number of mixed episodes, mean (SD)f

0.6 (1.6)

0.8 (1.3)

0.8

0.4

Illness duration, mean (SD)

22.5 (12.8)

13.5 (8.6)

−4.9

<0.0001

Lifetime comorbidity with substance dependence (%)

15 (8.9)

4 (7.3)

0.1

0.7

Lifetime comorbidity with alcohol dependence (%)

10 (5.9)

1 (1.8)

1.5

0.2

Presence of suicidal behaviour (%)

47 (28)

11 (20)

1.4

0.2

Type of clinical course cycle

 MDI (%)

75 (44.4)

22 (40.0)

3.7

0.45

 DMI (%)

20 (11.8)

11 (20.0)

 Irregular cycling (%)

65 (38.5)

21 (38.2)

 Continuous cycling (%)

5 (3.0)

1 (1.8)

 Rapid cycling (%)

4 (2.4)

0 (0.0)

Clinical variable

Bipolar disorder type 2 (N = 279)

χ 2 or t

p

Early onset (N = 142)

Late onset (N = 137)

Female (%)

85 (59.9)

80 (58.4)

0.06

0.8

Age at interview, mean (SD)

42.8 (14.4)

58.7 (10.1)

10.6

<0.0001

Presence of family history of any psychiatric disorder (%)

93 (65.5)

87 (63.5)

0.1

0.7

Presence of family history of mood disorder (%)b

84 (60.0)

79 (58.5)

0.06

0.8

Presence of family history of bipolar disorder (%)

36 (25.4)

19 (13.9)

5.8

0.02

Number of manic/hypomanic episodes, mean (SD)d

4.3 (4.2)

3.7 (4.3)

−1.1

0.3

Number of depressive episodes, mean (SD)e

6.0 (5.6)

5.4 (5.3)

−1.0

0.3

Illness duration, mean (SD)g

22.0 (13.7)

17.8 (11.2)

−2.8

0.005

Lifetime comorbidity with substance dependence (%)

8 (5.6)

6 (4.4)

0.2

0.6

Lifetime comorbidity with alcohol dependence (%)

19 (13.4)

6 (4.4)

6.9

0.01

Presence of suicidal behaviour (%)

45 (31.7)

29 (21.2)

3.9

0.06

Type of clinical course cycle

 MDI (%)

51 (35.9)

45 (32.8)

3.9

0.4

 DMI (%)

31 (21.8)

35 (25.5)

 Irregular cycling (%)

58 (40.8)

52 (38.0)

 Continuous cycling (%)

2 (1.4)

2 (1.5)

 Rapid cycling (%)

0 (0.0)

3 (2.2)

  1. Significant values are typed in italics
  2. MDI (hypo)mania-depression-free interval, DMI depression-(hypo)mania-free interval, SD Standard Deviation, p p value
  3. a BD1: missing data for 1 patient
  4. b BD1: missing data for 12 patients, BD2: missing data for 4 patients
  5. c BD1: missing data for 1 patient
  6. d BD1: missing data for 1 patient, BD2: missing data for 4 patients
  7. e BD1: missing data for 1 patient, BD2: missing data for 4 patients
  8. f BD1: missing data for 1 patient, BD2: missing data for 3 patients
  9. g BD2: missing data for 2 patients