Fig. 4.
nsample = 148. Average noise reduction (dB or dBA) as a function of strigency index score (Oxford University, 2022). It shows the trends in the common acoustical parameters, denoted as regression lines. Each symbol represents a sample mean of the noise level reduction identified and/or calculated from the 31 individual studies. A monotonic reduction in 24-h continuous (all-time) (Leq, 24h, Lden, Ldn), daytime (Ld: 6:00–18:00), and evening-time (Le: 18:00–22:00) levels by increasing severity levels of the COVID-19 confinements from pre to during the COVID-19 periods, while night-time level (Ln: 22:00–6:00) reductions were less apparent. The slopes of the regression lines and their statistical significance can be found in Table 2.