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# Chi squared calculations

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I handed in this problem to my professor and he commented that it is correct except for the chi squared calculations. I have rechecked 4 times and I get the same answer. Do you know what I did wrong?

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The expert examines the calculations for the chi square tests.

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Please see attachment! See calculations with red color!

The following observations are recorded:

Diet A Diet B Total

Cancer 30(a) 60(b) 90 (a+b)

No Cancer 353 (c) 357(d) 710 (c+d)

Total 383 (a+c) 417(b+d) 800(a+b+c+d)

Df= (r-1)(k-1)= (2-1)(2-1)= 1

A. Assume these are prospective data.

Please formulate an appropriate null hypothesis addressing whether diet affected the development of cancer, evaluate that null hypothesis, draw conclusions, and apply statistical inference, if appropriate (show all calculations explicitly). (5 points)

Ho: cancer is independent of diet; RRcancer = 1.0;  = 0.05
H1: the development of cancer will be affected by differences between diets A and B

Probability of cancer, diet A: a/(a + c) = 30/383 = 0.0783
Probability of cancer, diet B: b/(b + d) = 60/417 = 0.1439

Relative Risk ratiocancer = RRcancer = [a/(a + c)]/[b/(b + d)] = 0.0783/ 0.1439= 0.5441

Ea = [(a + ...

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• BSc , Wuhan Univ. China
• MA, Shandong Univ.
###### Recent Feedback
• "Your solution, looks excellent. I recognize things from previous chapters. I have seen the standard deviation formula you used to get 5.154. I do understand the Central Limit Theorem needs the sample size (n) to be greater than 30, we have 100. I do understand the sample mean(s) of the population will follow a normal distribution, and that CLT states the sample mean of population is the population (mean), we have 143.74. But when and WHY do we use the standard deviation formula where you got 5.154. WHEN & Why use standard deviation of the sample mean. I don't understand, why don't we simply use the "100" I understand that standard deviation is the square root of variance. I do understand that the variance is the square of the differences of each sample data value minus the mean. But somehow, why not use 100, why use standard deviation of sample mean? Please help explain."
• "excellent work"
• "Thank you so much for all of your help!!! I will be posting another assignment. Please let me know (once posted), if the credits I'm offering is enough or you ! Thanks again!"
• "Thank you"
• "Thank you very much for your valuable time and assistance!"

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