问题 问答题

简述方差分析的基本条件。

答案

参考答案:

(1)总体正态分布:

方差分析同Z检验及t检验一样,也要求样本必须来自正态分布的总体。在心理与教育研究领域中,大多数变量是可以假定其总体服从正态分布,一般进行方差分析时并不需要去检验总体分布的正态性。当有证据表明总体分布不是正态时,可以将数据做正态转化,或采用非参数检验方法。

(2)变异是可加的:

作为一种统计方法,方差分析把实验数据的总变异分解为若干个不同来源的分量。不同来源的变异只有当它们可加时,才能保证总变异分解的可能。变异是可加的即方差具有可分解性,就是将总平方和分解为几个不同来源的平方和。

(3)各处理内(即实验组内部)的方差一致:

在进行方差分析时,要求各实验组内部的方差彼此无显著差异,这是最为重要的一个条件,为了满足这一假定条件,往往在做方差分析前首先要对各组内方差做齐性检验。这与t检验中方差齐性检验的目的意义相同,只有处理内方差一致时,才能够进行比较,只是在具体方法上由于要比较的样本方差多于两个而有所不同。

问答题
单项选择题

Few creatures on earth are as cute as the black lion tamarin, and few have as dramatic a story line. Pug-nosed and diminutive, with a comic fringe of hair, these monkeys dwell in trees in small tracts of forest in southeastern Brazil. Or they did until 1905, when they were declared extinct. No one saw a black lion tamarin again in the wild until 1970. Later, in the 1990s, some Brazilian researchers turned up a small set of isolated, inbred populations scattered over a wide region. Since that time, they have been engineering tamarin migration, doing everything they can to save the world’s most distinctive primates.
Although they are no larger than house cats, tamarins have brains big for their size and a family life organized like our own. They live in groups anchored by an adult male andadult female, along with their offspring. When a mother bears young, she usually produces twins, and although members of the group share in their upbringing, it is most often the father who carries them around in the trees, where the families feed on fruits, insects and bird’s eggs.
Unhappily for the lion tamarins, their tree-bound niche began to disappear after the Portuguese landed in Brazil and began clearing forest to make room for Rio de Janeiro, the settlements and farms. As is the case for so many threatened species, the breakup of their habitat sounded the death knell for tamarins, depriving them of the continuity of forest they require to remain abundant and safe from potential threats in any single vicinity. The animals avoid predators by hardly ever coming down from the trees, so even a narrow logging road through a forest can begin the breakup by preventing them from moving from one patch of forest to another.
A simple solution was to build bridges across roads, allowing the monkeys to move from one forest to another. With some lumber and the researchers’ work, habitats that had been separated became continuous again, improving opportunities for migrating and mating.
The next step was to broaden the distribution of the population. The researchers captured two families of black lion tamarins and moved them to a new forest. After a year, the moves were declared a success: Not only had 80 percent of the tamarins survived, but they had also produced new offspring. So far, so good. The researchers had learned the animals could adjust to the new habitats, even if the insects there tasted a little different or the trees were a slightly different size.
The techniques for saving species in the wild vary. Species with less stringent habitat requirements, like wild turkeys, have been rescued by moving them into new settings as well as outlawing their killing. More challenging to preserve are species that require a lot of land, like elephants, and species that have highly specific requirements for habitat and prey -- like black-footed ferrets. Ultimately, as in all challenges, knowledge is power to save wild species from extinction.

The lumber bridges were devised to ______.

A.improve chances for tamarins to meet and mate

B.connect once separated habitats for the sake of research

C.make use of some lumber cut down

D.both A and C