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→分层内的区块随机试验 Block randomization within strata
===分层内的区块随机试验 Block randomization within strata===
===分层内的区块随机试验 Block randomization within strata===
'''<font color="#ff8000"> 区块随机试验 Block randomization </font>'''，有时称为置换区块随机试验，应用区块将来自同一阶层的受试者平均分配到研究中的每个组。 在区块随机试验中，指定了分配比率（一个特定组与其他组的数量之比）和组大小。 块大小必须是处理次数的倍数，以便每个层中的样本可以按预期比例分配到处理组。<ref name=":0" />例如，在一项关于乳腺癌的临床试验中，应该有 4 或 8 个层次，其中年龄和淋巴结状态是两个预后因素（prognostic factors），每个因素分为两个水平。 可以通过多种方式将不同的区块分配给样本，包括随机列表（random list）和计算机编程。
'''<font color="#ff8000"> 区块随机试验 Block randomization </font>'''，有时称为置换区块随机试验，应用区块将来自同一阶层的受试者平均分配到研究中的每个组。 在区块随机试验中，指定了分配比率（一个特定组与其他组的数量之比）和组大小。 块大小必须是处理次数的倍数，以便每个层中的样本可以按预期比例分配到处理组。<ref name=":0" />例如，在一项关于乳腺癌的临床试验中，应该有 4 或 8 个层次，其中年龄和淋巴结状态是两个预后因素（prognostic factors），每个因素分为两个水平。 可以通过多种方式将不同的区块分配给样本，包括随机列表（random list）和计算机编程。<ref>{{Cite web|url=https://www.sealedenvelope.com/help/redpill/latest/block/|title=Sealed Envelope {{!}} Random permuted blocks|date=Feb 25, 2020|website=www.sealedenvelope.com|access-date=2020-04-07}}</ref><ref>{{Citation|last1=Friedman|first1=Lawrence M.|title=Introduction to Clinical Trials|date=2010|work=Fundamentals of Clinical Trials|pages=1–18|publisher=Springer New York|isbn=978-1-4419-1585-6|last2=Furberg|first2=Curt D.|last3=DeMets|first3=David L.|doi=10.1007/978-1-4419-1586-3_1}}</ref>
Block randomization is commonly used in the experiment with a relatively big sampling size to avoid the imbalance allocation of samples with important characteristics. In certain fields with strict requests of randomization such as clinical trials, the allocation would be predictable when there is no blinding process for conductors and the block size is limited. The blocks permuted randomization in strata could possibly cause an imbalance of samples among strata as the number of strata increases and the sample size is limited, For instance, there is a possibility that no sample is found meeting the characteristic of certain strata.
Block randomization is commonly used in the experiment with a relatively big sampling size to avoid the imbalance allocation of samples with important characteristics. In certain fields with strict requests of randomization such as clinical trials, the allocation would be predictable when there is no blinding process for conductors and the block size is limited. The blocks permuted randomization in strata could possibly cause an imbalance of samples among strata as the number of strata increases and the sample size is limited, For instance, there is a possibility that no sample is found meeting the characteristic of certain strata.