Research has found that circumcision has a protective effect and helps prevent HIV in men who have sex with women, but circumcision does not seem to have the same protective effect helping to prevent HIV in men who have sex with men. This is an example of which of the following? A) Confounding B) Effect modification C) Selection bias D) Recall bias

In a study of factors that influence brand switching by a certain demographic, the following factors were identified as being significant as judged by the responses of the 439 participants in the survey. 1: Better price 2: Friend's recommendation 3: Seeing others use it 4: Interesting packaging 5: Buzz—people talking about the brand 6: An advertisement 7: Press stories 8: Entertainer/sports celebrity endorsement The results of the survey follow. Factor 1 2 3 4 5 6 7 8 Respondents (%) 68.6 60.2 22.8 20.6 16.6 16.6 14.7 6.9 Let A denote the set of factors that had a response greater than 20%, let B denote the set of factors that had a response between 15% and 25%, and let C denote the set of factors that had a response less than 25%. Find the following. (a)     n(A), n(B), n(C) n(A) =   n(B) =   n(C) =   (b)     n(A ∩ B) (c)     n(Ac ∩ C) (d)     n(A ∩ Bc) (e)     n(Ac ∩ Cc) (f)     n[(A ∪ B) ∩ C]

Five percent of the customers who visit a website complete a product purchase.  If one considers just the set of customers who completed the project purchase at the website, 80% read at least some of the user reviews about the product on the site.  When considering those customers who did not purchase of the product at the website, only 20% of these potential customers read the user reviews about the product on the site. The website managers are interested in how customer review-reading behavior affects the likelihood of purchase. A likelihood probability for this problem context is: A. P(Purchase | Visit Site) B. P(Did Not Purchase | Read User Reviews) C. P(Visit Site | Purchase) D. P(Did Not Read User Reviews | Product Purchased) E. None of the answers are correct.

A researcher is studying the effects of choices made by students entering middle school on future SAT outcomes. The researcher records the math course that the student enrolls in upon entering the sixth grade. The researcher uses SAT data for the same group of students, grouping students by college readiness. The data is displayed below.   College+Ready Likely+College+Ready Not+College+Ready Grade-level 20 96 85 Honors 48 134 101 Accelerated 8 23 16 Do the data suggest that sixth grade math enrollment and SAT college readiness are related? Use a 5% level of significance. a. Calculate the p-value (Rounded to 4 or more decimal places):____________ b. If the two variables were independent, what is the expected number of students who entered sixth grade in an honors math class and who obtained college ready designation based on the SAT?______________Rounded to 2 decimal places) c. What is the contribution to the chi-squared test statistic for this cell (from part…

Random digit dialing telephone surveys used to exclude cell phone numbers. If the opinions of people who have only cell phones differ from those of people who have landline service, the poll results may not represent the entire adult population. The Pew Research Center interviewed separate random samples of cell-only and landline telephone users who were less than 30 years old. Here’s what the Pew survey found about how these people describe their political party affiliation.     Do we reject, or fail to reject, the null hypothesis?