问题 问答题

请分析显著性水平对假设检验所犯错误概率大小的影响。

答案

参考答案:

解析:假设检验中所犯的错误有Ⅰ类错误和Ⅱ类错误。 Ⅰ类错误指的是虚无假设H0本来是正确的,但拒绝了H0;Ⅱ类错误指的是虚无假设本来不正确但却接受了H0。一个好的检验应该在样本容量n一定的情况下,使犯这两类错误的概率。和p都尽可能小,但。不能定得过低,否则会使p大为增加。在实际问题中,一般总是控制犯工类错误的概率α使H0成立时犯Ⅰ类错误的概率不超过α。在这种原则下的统计检验问题称为显著性检验,将犯I类错误的概率。称为假设检验的显著性水平。当假设检验的显著性水平增大时,犯I类错误的可能性就会提高,相应的犯Ⅱ类错误的可能性就会降低。反之亦然。

单项选择题

阅读理解:请根据短文内容,为每题确定l个最佳选项。

The National Trust。

The National Trust in Britain plays an increasingly important part in the preservation for public enjoyment of the best that is left unspoiled of the British countryside. Although the Trust has received practical and moral support from the Government, it is not a rich government department. It is a voluntary association of people who care for the unspoiled countryside and historic buildings of Britain. It is a charity which depends for its existence on voluntary support from members of the public. Its primary duty is to protect places of great natural beauty and places of historical interest.

The attention of the public was the first drawn to the dangers threatening the great old houses and the castles of Britain by the death of the Lord Lothian, who left his great seventeenth-century house to the Trust together with the 4500-acre park and estate surrounding it. This gift attracted wide publicity and started the Trust’s “Country House Scheme” Under this scheme, with the help of the Government and the general public, the Trust has been able to save and make accessible to the public about 150 of these oil houses. Lats year, about 1.75 million people paid to visit these historic houses, usually at a very small charge.

In addition to country houses and open spaces, the Trust now owns some examples of ancient wind and water mills, nature reserves, 540 farms and nearly 2500 cottages or small village houses, as well as some complete villages. In these villages no one is allowed to build, develop or disturb the old village environment in any way and all the houses are maintained in their original 16th century style. Over 4,000 acres of coastline , woodland, and hill country are protected by the Trust and no development or disturbances of any kind are permitted. The public has free access to these areas and is only asked to respect the peace, beauty and wildlife.

Over the past 80 years the Trust has become a big and important organization and an essential and respected part of national life. It helps to preserve all that and of historical significance not only for future generations of Britons but also for the millions of tourists who each year invade Britain in search of a great historic and cultural heritage.

All the following can be inferred from the passage EXCEPT______.

A.The Trust is more interested in protecting the 16th century houses.

B.Many people came to visit the historic houses saved by the Trust.

C.Visitors can get free access to some places owned by the Trust.

D.The Trust has a story which is longer than 80 years.

单项选择题 B1型题