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Question: The US National Toxicity Program studies the toxic...

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The US National Toxicity Program studies the toxicity and carcinogenicity of agents potentially causing a risk to human health. Electromagnetic fields around electrical installations are harmless in theory, but they might have a long-term effect on health – for instance, in triggering tumors. Observational studies in human populations have suggested a potential association. One study looked at the occurrence of cancers in otherwise healthy rats after 2 years of daily exposure to 60-hertz electromagnetic fields. Several groups were studied, each exposed to different electromagnetic intensity, as well as a control group kept in the same conditions but not exposed to any electromagnetic field. Here are the number of rats with a tumor after the 2 year study period for the control group and for the group exposed to 2 gauss, which is approximately 1000-fold the intensity level considered high exposure for humans:

treatment                                           male rats                                female rats

control: no exposure                           16 (n = 99)                            19 (n = 100)

2 gauss exposure                                30 (n = 100)                          22 (n = 100)

Find the P value using the normal curve.                                                                               1 point

Based on the P value, state your conclusion, using = .05 as the criterion for statistical significance.                                                                                                                          1 point

Explanation / Answer

We used chi-sq test for indepnedence:

H0: there is no impact of gender of rats on exposure

Ha: Ho is not true

Formula:

Male rat Female rat No exposure 16 19 35 2 guass exposure 30 22 52 46 41 87 Expected Male rat Female rat No exposure 19 16 2 guass exposure 27 25 Chi-sq Male rat Female rat No exposure 0.34 0.38 2 guass exposure 0.23 0.26 Chi-sq= 1.20 deg of freedom= 2 P-value= 0.547569 >0.05; cant reject H0

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