Figure 4

Trends in QIs RE model estimates (\({\tau }^{2}\)) from 2019 to 2023 by bootstrap method. This graph shows the trend in the estimated values of each Quality Indicator (QI) \({\tau }^{2}\) from 2019 to 2023 based on 500 bootstrap samples. Each line represents the \({\tau }^{2}\) estimate for a single bootstrap sample for an indicator in a different year. The clustering of the lines for each quality indicator suggests that the bootstrap sampling results are robust and stable over time.