问题 问答题

简述外部效度的影响因素。

答案

参考答案:外部效度亦称生态效度。
以人的行为为对象所获得的实验结果,其推论往往具有相当大的局限性。因此,实验的外部效度就要受到很多因素的制约。主要有以下三个方面的影响:
(1)实验环境的人为性。实验是在严格的控制条件下进行的,实验环境的人为性可能使某些实验结果难以用来解释日常生活中的行为现象。要改变这些因素的影响,可以提高实验情景与现实情景的相似性。一般来说,这种相似性越高,实验结果的可推广性也越高。
(2)被试样本缺乏代表性。从理论上讲,参与实验的被试必须具有代表性,必须从将来预期推论、解释同类行为现象的总体中进行随机取样。但实际上这很难做到。
(3)测量工具的局限性。实验者对自变量和因变量的操作性定义往往是以所使用的测量工具的测量结果来加以考虑的。

单项选择题 B1型题
单项选择题

Electronic mail has become an extremely important and popular means of communication.

The convenience and efficiency of electronic mail are threatened by the extremely rapid growth in the volume of unsolicited commercial electronic mail. Unsolicited commercial electronic mail is currently estimated to account for over half of all electronic mall traffic, up from an estimated 7 percent in 2001, and the volume continues to rise. Most of these messages are fraudulent or deceptive in one or more respects.

The receipt of unsolicited commercial electronic mail may result in costs to recipients who cannot refuse to accept such mail and who incur costs for the storage of such mail, or for the time spent accessing, reviewing, and discarding such mail, or for both. The receipt of a large number of unwanted messages also decreases the convenience of electronic mall and creates a risk that wanted electronic mail messages, both commercial and noncommercial, will be lost, overlooked, or discarded amidst the larger volume of unwanted messages, thus reducing the reliability and usefulness of electronic mail to the recipient. Some commercial electronic mail contains material that many recipients may consider vulgar or pornographic in nature.

The growth in unsolicited commercial electronic mail imposes significant monetary costs on providers of Internet access services, businesses, and educational and nonprofit institutions that carry and receive such mail, as there is a finite volume of mail that such providers, businesses, and institutions can handle without further investment in infrastructure. Many senders of unsolicited commercial electronic mail purposefully disguise the source of such mall.

Many senders of unsolicited commercial electronic mall purposefully include misleading information in the messages’ subject lines in order to induce the recipients to view the messages. While some senders of commercial electronic mail messages provide simple and reliable ways for recipients to reject (or ’opt-out’ of) receipt of commercial electronic mall from such senders in the future, other senders provide no such ’opt-out’ mechanism, or refuse to honor the requests of recipients not to receive electronic mail from such senders in the future, or both.

Many senders of bulk unsolicited commercial electronic mail use computer programs to gather large numbers of electronic mail addresses on an automated basis from Internet websites or online services where users must post their addresses in order to make full use of the website or service.

The problems associated with the rapid growth and abuse of unsolicited commercial electronic mall cannot be solved by the government alone. The development and adoption of techno-logical approaches and the pursuit of cooperative efforts with other countries will be necessary as well.

According to the passage, efficiency of e-mail is threatened by ().

A. heavy e-mail traffic

B. fraudulent e-mail messages

C. large volume of messages

D. increasing amount of unwanted e-mail