trained to sit if a breath sample came from a cancer patient. After training, th
ID: 3313221 • Letter: T
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trained to sit if a breath sample came from a cancer patient. After training, the dogs were presented with breath samples from new subjects, with the samples randomly presented in a double-blind environment. The study was done for patients who were in differ ent stages of cancer and for lung and breast cancer patients The results for all groups were similar. The data for early-stage breast cancer are presented in Table B.1. (a) Discuss the data collection for this study. Why is it important that the samples are from new subjects whose samples the dogs have not encountered before? That they are randomly presented? That the study is double-blind? That patients have not yet started treatment? Do you think this experiment was well designed? (b) In the study for lung cancer, the experimenters had to account for the effect of smoking. Why? (c) The question of interest is whether dogs are more likely to sit if the subject has cancer than if the subject does not have cancer. State the null and alternative hypotheses and give the relevant sample statistics. (d) Without doing any computations, just look- ing at the data, do you expect the p-value to be relatively large or relatively small? Why? How strong is the evidence? (Sometimes, in extreme cases such as this one, we see results so obvious that a formal test may not be nec- essary. Unless results are exceptionally obvious however, you should confirm your intuition with statistical inference.) Table B.1 Can dogs smell cancer? Control Cancer Dog docsn't sit Dog sits 45 B.2 Can Dogs Smell Cancer? Can dogs provide an easy noninvasive way to detect cancer? Several methods have been used to test this. In a recent study.0 five dogs were trained over a three-week period to smell cancer in breath samples. To collect the data, cancer patients who had just been diag- nosed and had not yet started treatment were asked to breathe into a tube. Breath samples were also collected from healthy control adults. Dogs were 50McCulloch, M., et al., "Diagnostic Accuracy of Canine Sceat Detection in Early- and Late-Stage Lung and Breast Cancers Integrative Cancer Therapies, 200S(1 ) -39.Explanation / Answer
a) It is important that the samples are from new subjects whose samples the dogs have not encountered before as it will prevent biasness.
Randomly presenting and double blind is to remove any biasness. This experiment is well designed as it has taken every precation to avoid biasness in collecting data.
b)The experimenters had to account for the effect of smoking because smoking causes cancer.
c) Null Hypothesis: There is no association between Dog sit and having cancer.
Alternative Hypothesis: Their is a significant assocoation between Dog sit and having cancer.
d) Just by looking at the data my guess is p-value is going to relatively small, confirming significant association between Dog sit and having cancer.
Let's do chi-square test to find that.
Pearson's Chi-squared test with Yates' continuity correction
data: c
X-squared = 110.96, df = 1, p-value < 0.000
Conclusion : Since the calcullated p-value is 0.000 which is less than 0.05 , we can conclude that there is a significant association between dog sit and having cancer.
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