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Quiz3Sols

# Quiz3Sols - conclusion that playing violent video games is...

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Quiz 3 Solutions 1a) Original problem: pred y in SU: -2 x 0.6 = -1.2 so predict 1.2 SDs below avg. Rms error: sqrt(1-0.6^2) x SD = 0.8 SD. 4 th percentile is 1.75 SDs below avg. So in the vert strip, we have [(-1.75 SDy + avg)–(-1.2 SDy +avg)]/0.8SDy = -0.69 Area to the left is 14%. New problem: predict 1.2 SDs below avg, the 11.5 th percentile 1b) predicted final score = (-2)(.6)(10) + 50 = 38 z = (50-38)/(10(.8)) = 1.5 (100-86.64)/2 = 6.68% 1c) predicted final score = (1)(.6)(10)+50 = 56 z = (80 - 56)/(10(.8)) = 3 (100 - 99.73)/2 = .135% 2a) Observational study Possible explanation: “Students aren’t assigned to treatment/control by the investigators.” “Students are self-selected to be in treatment or control.” “We just observe what the students do.” 2b) The conclusion is too strong. “Association is not causation,” or “There may be confounding factors.” Since this was an observational study, we can say that the data supports the
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Unformatted text preview: conclusion that playing violent video games is associated with poor academic performance and bad behavior, but we cannot say that violent video games leads to these things happening. 3a) mean(x) = 23.83 mean(y) = 255.66 sd(x) = 14.22 sd(y) = 165.48 sumxy = 48410, r = .839 m = (165.48/14.22)*.839 = 9.77 b = 255.66 - 23.83*9.77 = 22.81 Pred Y = 9.77(x) + 22.81 3b) Pred Y = 9.77(22)+22.81 = 237.75 or approx 238. 3c)Doesn’t make sense. Correlation does not imply causation, basically same as 2b). (Note that this is not ecological correlation since we’re not calculating averages or medians, what we’re interested in is actually data for cities.) Size of the city is a likely confounding factor. Bigger cities in general have more Burger King restaurants and homicides than smaller cities....
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