现有八家百货公司，每公司人均月销售额和利润率资料如下：
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若用最小二乘法以利润率为因变量拟合得到的回归方程为Y=-0.852+0.002X，说明（）。
A．X与Y之间存在着负相关关系
B．每人每月销售额X增加一元，则利润率Y就会提高0.002%
C．每人每月销售额X增加一元，则利润率Y就会平均提高0.002%
D．X与Y之间存在着显著的线性相关关系
参考答案：C
解析：
A项，在一元线性回归方程中，回归系数
与相关系数r的符号一致，故X与Y之间存在着正相关关系；C项，回归系数
表示自变量每变动一个单位量时，因变量的平均变化量，故
=0.002表示每人每月销售额X增加一元，则利润率Y就会平均提高0.002%；D项，F检验统计值未知，故无法判断X与Y之间是否存在着显著的线性相关关系。
Passage Three
| Watching movie stars light up on screen may increase the odds a child or young teen will try smoking, study findings suggest. In this latest study, researchers at Dartmouth Medical School in Lebanon, New Hampshire found that the odds of a child smoking increased in tandem (一前一后，紧密相连) with the number of films with smoking scenes he or she had seen. This pattern remained regardless of other smoking risk factors such as having parents or friends who smoked, poor school performance or a self-reported "rebellious" nature. Dr. James D. Sargent and his colleagues report the findings in the December 15th issue of the British Medical Journal. In response to the findings, the British Medical Association (BMA) called on the UK film industry to "stub out" on-screen smoking. "When smoking is glamorized in movies, young people are encouraged to experiment with a lethal (致命的) habit," the BMA’s Dr. Vivienne Nathanson said in a statement. And an editorial accompanying the journal report made the same challenge to Hollywood. "It is time for the entertainment industry to accept responsibility for its actions and stop serving the interests of tobacco companies," writes Dr. Stanton A. Glantz of the University of California, San Francisco. Sargent’s team based the findings on a survey of nearly 5 000 Vermont and New Hampshire students aged 9 to 15. Students were asked whether they had seen any of 50 recent movies that the researchers had screened for the number of smoking scenes. They also answered questions about environmental risk factors for smoking, their personality traits and perceptions of their parents’ views on smoking. The investigators found that the number of smoking instances students had seen in the movies was correlated with their odds of having tried smoking. Kids who had seen 51 to 100 smoking occurrences were 70% more likely than those who had seen fewer to have smoked. And the odds were nearly three times greater among those who had seen 150-plus smoking scenes. According to the researchers, the effects of on-screen smoking were similar to those of having parent or sibling who smoked. "The results indicate that exposure to tobacco use in films is pervasive," Sargent’s team writes. "More importantly, such exposure is associated with trying smoking, which supports the hypothesis that films have a role in the initiation of smoking. " In his editorial, Glantz agrees, writing that the study "provides powerful new evidence" that smoking in movies does contribute to adolescent smoking. |
The passage mainly conveys the idea that ______.
A．movie stars smoking on screen may initiate children to imitate them
B．violence on screen may lead youth to form bad behaviors
C．media play the most important role in influencing children’s beliefs and actions
D．whether on-screen smoking can lead children to smoking has not yet been proved