【DS6371】statistics

                                                       

1. (1pt each unless otherwise noted) True / False and Short Answer….  Simply Highlight “True” or “FALSE” or write in the answer where appropriate.

1. 1. True / False We must sample more than 30 subjects from a population in order for the sampling distribution of the sample mean to have a normal distribution.  
   2. True / False For a two-sided, two sample pooled confidence interval for the difference in means (µ1-µ2), if this confidence interval is (-4,-1) this is evidence that µ1 is larger than µ2
   3. True / False The Rank-Sum test is resistant to outliers.
   4. True / False We wish to test the equality of 2 group means. If the normality assumption is met, the two sample t-test is robust to the standard deviation assumption as long as the sample sizes of the groups are the same.   
   5. True / False In a randomized experiment, where the subjects are randomly assigned to the treatment groups, the result can always be generalized to the population the sample is taken from.
   6. True / False Adding an interaction term between a categorical and continuous variables in a regression model allows the possibility for different slopes for different levels of the categorical variable.  
   7. True / False We will need 7 indicator variables to code a categorical variable with 7 levels.  
   8. True / False The model with the lowest AIC will always have the lowest external cross validation ASE (ASE on the test set).  
   9. True / False In regression, for a fixed value of the explanatory variable, the prediction interval for the response can be narrower than the confidence interval for the mean response.
   10. True / False Assume we take a sample and find a 95% confidence interval for the mean to be (5,9). If we conduct a hypothesis test for  on the same data, the pvalue will be less than .05.  
   11. Multiple Choice 2pts If a variable that is independent of the response is included in the model because its pvalue is less than alpha, what type of error has been made?

1. 1. Type I Error b. Type II Error  c. No Error has been made

1. 1. Short Answer 2pts: In regression, the confidence interval and prediction interval for the response are narrower for different values of the explanatory variable.  At what value of the explanatory variable are the confidence interval and prediction interval the narrowest?  

Answer: Confidence interval and prediction interval are narrowest at the mean

1. 1. (2 pts) Your company is trying out a new website to try and generate more business.  Assume your boss has asked you to compare the mean daily mouse click traffic on the company’s 5 different versions of its new website: Original Version, Ver 1, Ver 2, Ver 3, Ver 4.  You were asked to compare the mean click rate between each new website (Ver 1, Ver 2, Ver 3 and Ver 4) and the original website (Original Website).   You of course want to do the appropriate multiple comparison correction.  Which correction is most appropriate here?  

Select one:

1. Dunnett
2. Tukey-Kramer
3. Bonferroni

1. Matching (1 pt each) Letters can be used more than once!