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Unformatted text preview: NAME (Please Print): KEY HONOR PLEDGE (Please Sign): Statistics 101 Midterm 1 This is a closed book exam. You may use your calculator and a single page of notes. The room is crowded. Please be careful to look only at your own exam. Try to sit one seat apart; the proctors may ask you to randomize your seating a bit. Report all numerical answers to at least two correct decimal places or (when appro priate) write them as a fraction. All question parts count for 1 point. 1 C 1. A weighted average A: is an ecological correlation. B: is often used in randomized controlled experiments. C: can control for a confounding factor. D: two of the above. E: none of the previous. 2. The tables below show the relationship between ticket classes and survival on the Titanic. Women Survival Death First Class 140 4 Third Class 76 89 Men Survival Death First Class 57 118 Third Class 75 387 .62 (a) What was the overall survival rate for the first class? (140 + 57)/(140 + 4 + 57 +118) = .618 .54 (b) Use a weighted average to estimate the survival rate for the first class. 309 946 140 144 + 637 946 57 175 = . 537 (c) First class passengers show better survival than third class passengers. Was there class discrimination in survival of the wreck of the Titanic? Explain. Women in both classes tended to survive better than men, but upper class women had better survival than lower class women, and the same for men. If one com putes the weighted average survival rates for both classes, it is clear that first class passengers had precedence on the life boats. 3. List the three key features of a good experimental design. (a) controlled 2 (b) randomized (c) doubleblind D 4. Reserach using historical controls A: gives a placebo to the control group. B: involves a randomized experiment. C: controls for a confounding factor. D: none of the above. 5. An unfair coin is tossed 4 times. The probability of heads is .7. .3 Find the probability that the 4th toss is a tail given the first 3 are heads. Tosses are independent; the first 3 have no effect. .21 Find the probability that the third toss is a tail and the last toss is a head. By independence, P[A and B] = P[A] * P[B] = .3 * .7. .79 Find the probability that the third toss is a tail or the last toss is a heads....
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 Spring '08
 BURKHART

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