Bristol Medical School: Population Health Sciences, University of Bristol, Bristol, UK.
MRC Clinical Trials Unit, University College London, London, UK.
Res Synth Methods. 2019 Mar;10(1):113-124. doi: 10.1002/jrsm.1329. Epub 2018 Dec 4.
Network meta-analysis compares multiple treatments from studies that form a connected network of evidence. However, for complex networks, it is not easy to see if the network is connected. We use simple techniques from graph theory to test the connectedness of evidence networks in network meta-analysis. The method is to build the adjacency matrix for a network, with rows and columns corresponding to the treatments in the network and entries being one or zero depending on whether the treatments have been compared or not, and with zeros along the diagonal. Manipulation of this matrix gives the indirect connection matrix. The entries of this matrix determine whether two treatments can be compared, directly or indirectly. We also describe the distance matrix, which gives the minimum number of steps in the network required to compare a pair of treatments. This is a useful assessment of an indirect comparison as each additional step requires further assumptions of homogeneity in, for example, design and target populations of included trials. If there are no loops in the network, the distance is a measure of the degree of assumptions needed; it is approximately this with loops. We illustrate our methods using several constructed examples and giving R code for computation. We have also implemented the techniques in the Stata package "network." The methods provide a fast way to ensure comparisons are only made between connected treatments and to assess the degree of indirectness of a comparison.
网络荟萃分析比较了来自证据网络的多项研究中的多种治疗方法。然而，对于复杂的网络，很难看出网络是否连接。我们使用图论中的简单技术来检验网络荟萃分析中证据网络的连通性。该方法是构建网络的邻接矩阵，其中行和列对应于网络中的治疗方法，并且条目为 1 或 0，具体取决于治疗方法是否已进行比较，并且对角线为 0。对该矩阵的操作给出了间接连接矩阵。该矩阵的条目确定了两种治疗方法是否可以直接或间接进行比较。我们还描述了距离矩阵，该矩阵给出了比较一对治疗方法所需的网络中的最小步骤数。这是对间接比较的有用评估，因为每增加一个步骤都需要进一步假设包括试验的设计和目标人群的同质性。如果网络中没有环路，则距离是所需假设程度的度量；有环路时，距离大约是这个值。我们使用几个构造的示例说明了我们的方法，并提供了用于计算的 R 代码。我们还在 Stata 软件包“network”中实现了这些技术。这些方法提供了一种快速的方法，可以确保仅在连接的治疗方法之间进行比较，并评估比较的间接程度。
