那些试图追踪通过邮件传播的连锁信件受到选择性偏差的干扰，因为他们只包括了那些新闻组档案里过时的帖子。

Studies that tried to track how chain letters propagate by email suffered from selection bias because they included only posts that had been "fossilized" on newsgroup archives.

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评估者将80封信分为“自杀”和“没自杀”两组，内容表达悲伤的信件将被剔除。

The evaluators classified the 80 letters as' suicide 'or' no suicide 'in an intention-to-treat analysis. Letters expressing sadness were subsequently excluded for a per-protocol analysis.

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每一周，法庭以信件形式通知随机挑出的一组公民，请他们作为“陪审团候选人员”。

Each week the court sends a notice in the mail to a randomly selected group of citizens requiring service in the "jury pool".

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