Table 2 Efficacy and safety of aspirin compared to placebo in preventing VTE.

From: Aspirin for the extended prevention of venous thromboembolism: a meta-analysis and trial sequential analysis

Variable

RR

[95% CI]

z

P-value

τ 2

τ

I2

P at Q test

QoE

Efficacy

 VTE3,4,5,6,7

0.80

[0.72; 0.90]

− 3.58

< 0.001

0

0

42.0% [0.0%; 77.0%]

0.125

⊕⊕⊕⊖ Moderate†

 DVT3,4,5,6,7

0.82

[0.71; 0.95]

− 2.55

0.010

0

0

0.0% [0.0%; 74.6%]

0.439

⊕⊕⊕⊖ Moderate†

 PE3,4,5,6,7

0.79

[0.66; 0.95]

− 2.45

0.014

0

0

31.3% [0.0%; 72.1%]

0.201

⊕⊕⊕⊖ Moderate†

 All-cause mortality3,5,6,7

0.97

[0.86; 1.09]

− 0.44

0.655

0

0

0.0% [0.0%; 79.2%]

0.973

⊕⊕⊕⊖ Moderate‡

 Cardiovascular mortality3,5,6,7

0.92

[0.78; 1.08]

− 0.98

0.322

0

0

0.0% [0.0%; 79.2%]

0.840

⊕⊕⊖⊖ Low†‡

 VTE-related mortality3,5,6

0.44

[0.26; 0.75]

− 3.05

0.002

0

0

0.0% [0.0%; 84.7%]

0.877

⊕⊕⊕⊖ Moderate†

Safety

 Bleeding3,4,5,6,7

1.13

[1.10; 1.16]

10.41

< 0.001

0

0

12.2% [0.0%; 77.7%]

0.337

⊕⊕⊕⊖ Moderate†

 Major bleeding3,4,5,6,7

1.18

[1.07; 1.30]

3.31

< 0.001

0

0

0.0% [0.0%; 74.6%]

0.601

⊕⊕⊕⊖ Moderate†

 Trasfusion3,4

1.15

[0.86; 1.53]

0.95

0.337

0.046

0.216

63.5% [0.0%; 89.6%]

0.064

⊕⊕⊖⊖ Low*‡

 Stroke3,4,5,6,7

1.10

[0.86; 1.41]

0.81

0.417

0

0

0.0% [0.0%; 74.6%]

0.923

⊕⊕⊕⊖ Moderate‡

 Haemorrhagic stroke3,4

0.95

[0.26; 3.38]

− 0.07

0.936

0.449

0.670

26.9% [0.0%; 99.9%]

0.242

⊕⊕⊖⊖ Low*‡

 Major cardiovascular AEs3,4,5,6,7

0.92

[0.83; 1.03]

− 1.39

0.162

0.006

0.079

39.1% [0.0%; 75.8%]

0.145

⊕⊕⊖⊖ Low*‡

 Cardiac AEs3,5,6,7

1.03

[0.79; 1.35]

0.28

0.773

0.036

0.191

9.3% [0.0%; 81.1%]

0.353

⊕⊕⊖⊖ Low*‡

 Myocardial infarction3,5,6,7

1.03

[0.86; 1.24]

0.38

0.700

0.004

0.067

26.3% [0.0%; 70.7%]

0.246

⊕⊕⊖⊖ Low†‡

  1. RR relative risk, 95%CI 95% confidence interval, z z-score measures how many standard deviations a data point is from the mean, τ2 between-study variance in random-effects meta-analysis, τ standard deviation estimate of effect sizes in random-effects meta-analysis, I2 measures percentage variation across studies due to heterogeneity, Q test Cochran’s Q test assesses heterogeneity among study results, QoE quality of evidence. *Downgraded one level for inconsistency (such as heterogeneity of estimates of effects across trials)12. †Although a low I2 value usually suggests low heterogeneity, the quality of evidence for this observation remains uncertain. This uncertainty arises from a broad I2 confidence interval, which hints at potential undetected heterogeneity. Despite the reported absence of between-study variance (τ2 = 0) and no variation in effect estimates (τ = 0), and an I2 of 0%, the QoE for the outcome was prudently downgraded one level12. ‡Downgraded one level for Imprecision (for example, 95% confidence intervals are wide and include or are close to null effect)12 High QoE (⊕⊕⊕⊕): The authors are very confident that the true effect lies close to that of the estimate of the effect. Moderate QoE (⊕⊕⊕⊖): The authors are moderately confident in the effect estimate. The true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low QoE (⊕⊕⊖⊖): The authors’ confidence in the effect estimate is limited. The true effect may be substantially different from the estimate of the effect12.
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