Meta-analysis is an application of idea #4 (Bayesian Multilevel Models) in the article. What makes meta-analysis special within a multilevel framework is that

Meta-analysis is an application of idea #4 (Bayesian Multilevel Models) in the article. What makes meta-analysis special within a multilevel framework is that you know the level 1 variance. This creates a special case of a generalized multilevel model where you leverage your knowledge of L1 mean and variance (from each individual study's results) to estimate the possible mean and variance of the population effect. The population mean and variance is usually presented in funnel plots where you can see the expected distribution of effect sizes/point estimates given a sample size/standard error. Researchers have also started to plot actual point estimates from published papers in this plot, showing that most of the published results are "inside the funnel", a result that is usually cited as evidence of publication bias. In other words, the missing studies end up in researchers' file drawers instead of being published somewhere.