In general, the tests work most effectively when the qualities to be measured can be most precisely defined and least effectively when what is to be measured or predicted can not be well defined.

【参考答案】

一般的说，当所要测定的特征能很精确界定时，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。