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Table 2 Bivariable associations between trial characteristics and reporting of any exploration of subgroup analysis and reporting of subgroup analysis using appropriate methods

From: No improvement in the reporting of clinical trial subgroup effects in high-impact general medical journals

Characteristic

Number

Reports subgroup analysis, n (%) N = 270

Uses appropriate methods, n (%) N = 185

Journal of publication

 

p = 0.01

p = 0.22

 Annals

37

21 (57)

18 (86)

 British Medical Journal

48

21 (44)

12 (57)

 Journal of the American Medical Association

76

44 (58)

33 (75)

 Lancet

123

76 (62)

52 (68)

 New England Journal of Medicine

153

108 (71)

70 (65)

Year of publication

 

p = 0.27

p = 0.046

 2007

119

74 (62)

57 (77)

 2010

144

79 (55)

54 (68)

 2013–2014

174

117 (67)

74 (63)

Biostatistician as coauthor

 

p = 0.07

p = 0.38

 No biostatistician as coauthor

183

104 (57)

68 (65)

 Biostatistician as coauthor

254

166 (65)

117 (70)

Medical condition under study

 

p = 0.003

p < 0.001

 Cardiovascular

101

73 (72)

63 (86)

 Infectious disease

82

52 (63)

25 (48)

 Cancer

59

45 (76)

24 (53)

 Psychiatry/neurology

40

20 (50)

11 (55)

 Autoimmune, including diabetes

37

22 (59)

15 (68)

 Pulmonary/critical care

29

14 (48)

11 (79)

 Obstetrics/gynecological

21

10 (48)

8 (80)

 Other chronic disease

41

24 (59)

19 (79)

 Other, uncategorized

27

10 (37)

9 (90)

First author’s region

 

p = 0.14

p = 0.19

 North America

185

123 (66)

84 (68)

 Europe

188

113 (60)

82 (73)

 Other

64

34 (53)

19 (56)

Funding

 

p < 0.001

p = 0.005

 Industry funding

188

141 (75)

86 (61)

 No industry funding

249

129 (52)

99 (77)

Significance of the primary outcomea

 

p = 0.013

p = 0.003

 Not significant

153

106 (69)

85 (80)

 Significant

277

158 (57)

100 (63)

Study design

 

p = 0.002

p = 0.53)

 Parallel

425

268 (63)

18 (69)

 Crossover

12

2 (17)

1 (50)

Sample size

 

p < 0.001

p = 0.01

 Quintile 1 (median = 69)

88

29 (33)

13 (45)

 Quintile 2 (median = 234)

87

44 (51)

30 (68)

 Quintile 3 (median = 507)

88

58 (66)

39 (67)

 Quintile 4 (median = 1080)

87

65 (75)

48 (74)

 Quintile 5 (median = 5455)

87

74 (85)

55 (74)

  1. For articles that report on the appropriate use of methods for subgroup analysis, the denominator used is the number reporting any subgroup analysis
  2. Chi-square tests were used for categorical variables. In the case of small cells, we used Fishers exact test. A test for trend was used for the year and sample size
  3. an = 7 trials were excluded for not reporting a statistical test for the primary outcome
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