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Systematic reviews and meta‐analyses are principal tools to synthesize evidence from multiple independent sources in many research fields. The assessment of heterogeneity among collected studies is a critical step when performing a meta‐analysis, given its influence on model selection and conclusions about treatment effects. A common‐effect (CE) model is conventionally used when the studies are deemed homogeneous, while a random‐effects (RE) model is used for heterogeneous studies. However, both models have limitations. For example, the CE model produces excessively conservative confidence intervals with low coverage probabilities when the collected studies have heterogeneous treatment effects. The RE model, on the other hand, assigns higher weights to small studies compared to the CE model. In the presence of small‐study effects or publication bias, the over‐weighted small studies from a RE model can lead to substantially biased overall treatment effect estimates. In addition, outlying studies may exaggerate between‐study heterogeneity. This article introduces penalization methods as a compromise between the CE and RE models. The proposed methods are motivated by the penalized likelihood approach, which is widely used in the current literature to control model complexity and reduce variances of parameter estimates. We compare the existing and proposed methods with simulated data and several case studies to illustrate the benefits of the penalization methods. [ABSTRACT FROM AUTHOR]

Objective: Increased signal intensity (ISI) on T2-weighted magnetic resonance imaging (MRI) often indicates severe compression in patients with cervical myelopathy (CM). The optimal surgical approach for CM patients with ISI on T2-weighted MRI remains unclear. This meta-analysis aims to compare the clinical outcomes between anterior and posterior approaches for the treatment of these patients. Methods: MEDLINE, EMBASE, Web of Science, and Chinese National Knowledge Infrastructure (CNKI) were searched for relevant studies through January 2019. Statistical comparisons were made when appropriate. Results: A total of 9 studies (748 participants) out of 1066 citations were included in this study. All of the selected studies were high quality, as indicated by the Newcastle–Ottawa scale and the Cochrane Collaboration tool for assessing the risk of bias. Clinical outcomes were compared between anterior and posterior approaches in 4 studies (237 participants). The preoperative Japanese Orthopedic Association (JOA) score was similar between the two groups [P = 0.98, weighted mean difference (WMD) = 0.01 (− 0.58, 0.59)]. The postoperative JOA score [P < 0.05, WMD = 0.68 (0.06, 1.30)] and recovery rates [P < 0.01, WMD = 0.12 (0.06, 0.17)] were significantly higher in the anterior group than in the posterior group. Conclusion: The anterior approach was associated with better postoperative neural function than the posterior approach in CM patients with ISI on T2-weighted MRI. [ABSTRACT FROM AUTHOR]