Table 3.

Assessment of the Quality of Evidence

	Question: Are workers chronically exposed to noise at work with an exposure intensity of >80 dB(A) at an elevated risk for developing arterial hypertension?
№ of Studies (Participants)	1. Study limitations	2. Indirectness	3. Inconsistency	4. Imprecision	5. Publication Bias	6. Effect size	7. Dose-response Gradient	8. Residual Confounding	Effect Size	Certainty
23 observational studies (n = 171 985) 1	not serious 2	not serious	not serious 3	not serious	Detected4 ↓	Detected 5 ↑	Detected 6 ↑	no	RR 1.72 (1.48 to 2.01)	⨁⨁⨁ HIGH

¹ This is the total number of participants included in our main analysis, comprising of n = 111,796 noise exposed workers and 59,669 workers in comparison groups, as well as 40 cases and 480 control persons from the one case-control study; ² While a majority of the studies had a high risk of bias, considering the pooled effect of low risk of bias studies increased the risk estimate (RR 1.85; 95% CI 1.17–2.90); ³ Although the measured heterogeneity in the main analysis was substantial (I² > 50 %) and the χ² test of indicated heterogeneity (p < 0.001), the confidence limits overlapped, and the heterogeneity of homogenous subgroups was generally lower and sometimes I² < 50%; ⁴ The funnel plot indicated asymmetry; ⁵ The pooled effect of the main analysis (ES) did not exceed 2.0 (ES = 1.72; 95% CI 1.48–2.01; Figure 2), but ES in the subgroup of workers exposed to >85–≤90 dB(A) was 3.50 (95% CI 1.56–7.86); ⁶ The subgroup analysis of different noise exposure levels (Figure 3) and the descriptive depiction of studies considering several levels of noise indicate a dose-response gradient (Supplementary Figure S1).