In general, the tests work most effectively when the qualities to be measured can be mostprecisely defined and least effectively when what is to be measured or predicted can not bewell defined.
【分析】
多重复合句。and连接两个并列的状语most effectively 和 least effectively。两个 when引导时间状语从句,不定式短语to be measured作后置定语,修饰 the qualities;第二个when引导的时间状语从句,又嵌套what引导的主语从句。翻译时,按照汉语表达习惯,两个when引导的时间状语从句均前置,分别译于两个主句之前;to be measured译为the qualities的前置定语。
【译文】
一般地说,当所要测定的特征能很精确地界定时,测试最为有效;而当所要测定或预测的东西不能明确地界定时,测试的效果则最差。