Table 1

Descriptive statistics depicting the differences between groups NAC and placebo on demographic and illness characteristics.

Characteristics

Descriptive statistic

Total sample

n = 149

NAC

n = 76

Placebo

n = 73

Test statistic

Value

df

P


Age

M(SD)

45.8 (11.4)

47.1 (10.9)

44.4 (11.8)

t-test

1.46

147

.146

Gender %Female

% (n)

67.8 (101)

78.9 (60)

56.2 (41)

χ2

8.85

1

.003

Diagnosisa

Bipolar I disorder

% (n)

69.6 (103)

73.7 (56)

65.3 (47)

χ2

1.24

1

.266

Bipolar II disorder

% (n)

29.7 (44)

25.0 (19)

34.7 (25)

Bipolar NOS

% (n)

1 (0.7)

1.3 (1)

0.0 (0)

Suicidality %Yes

% (n)

70.9 (105)

69.7 (53)

72.2. (52)

χ2

0.11

1

.739

Age of first symptoms

M(SD)

22.0 (10.6)

22.2 (11.8)

21.9 (9.2)

t-test

0.17

138

.867

Age of diagnosis

M(SD)

35.9 (11.6)

37.4 (12.0)

34.4 (11.2)

t-test

1.58

141

.115

Duration of illness since diagnosis (years)b

M(SD)

10.0 (9.4)

9.6 (9.3)

10.5 (9.6)

t-test

-0.74

141

.462

Mdn

7.0

6.0

7.5

Number of psychiatric hospitalisationsc

M(SD)

3.0 (4.4)

3.2 (5.3)

2.8 (3.3)

t-test

-0.31

141

.759

Mdn

1.0

2.0

1.0

Number of manic episodes >10

% (n)

53.5 (76)

54.8 (40)

52.2 (36)

χ2

0.10

1

.754

Number of depressive episodes >10

% (n)

78.3 (112)

80.8 (59)

75.7 (53)

χ2

0.55

1

.459

Smoker %Yes b

% (n)

37.1 (49)

30.8 (20)

43.3 (29)

χ2

2.21

1

.137

Alcohol use %Yes b

% (n)

47.0 (62)

47.7 (31)

46.3 (31)

χ2

0.03

1

.870

Alcohol dependence/abuse b

% (n)

14.2 (21)

14.5 (11)

13.9 (10)

χ2

0.01

1

.919

Substance use %Yes b

% (n)

3.0 (4)

4.6 (3)

1.5 (1)

χ2

1.10

1

.295

Substance dependence/abuse b

% (n)

14.3 (21)

13.3 (10)

15.3 (11)

χ2

0.11

1

.736


aChi-square based on two categories (Bipolar I disorder versus other) due to small cell sizes;

b These substances use variables related to status at entry to the maintenance phase of the trial (Week 8). c Inferential statistics based on logarithmic transformed data (plus constant) because of extreme positive skewness. Untransformed descriptive statistics are reported.

Berk et al. BMC Medicine 2012 10:91   doi:10.1186/1741-7015-10-91

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