Answers to the Review questions from Homework 1
Review Exercise Answers (Chapter 2)
1. False, you need to know how many people fly by commuter airline vs. scheduled carriers. Only then can you compare rates. Scheduled carriers are safer when you look at it this way.
7. (a) observational study -- therefore confounding is a problem.
(b) rates of cervical cancer go up with age; women of different marital status have different patterns of sexual activity and therefore experience different risks; similar for education. All of these are potential confounders.
(c)Pill users are more sexually active than non-users and tend to have more partners. That seems to be what is causing the higher rate among pill users.
(d) no. see part (c)
8. No. What a silly statement. Memorial Day is the last weekend of May and Labor Day is the first weekend of September. 25% of days in the year fall in between. If burglars work the same amount every day -- we would expect at least 25% of the burlaries to occur in this time period --- whether or not you went on vacation...
12. False. This is just like the admission study on page 17 and a demonstration of Simpson's Paradox. The Democrats may be concentrated in wards with low turnout.
From Chapter 3 Review
2. (a) more at age 1 (b) more at age 31 (d) more at age 35-44 the rectangle has more area (d) 50%
7. (i) natural causes -- old people tend to die from these things
(ii) trauma -- younger people tend to be somewhat more reckless and have a better chance of dying in an accident, murder, suicide...
8. (a) True, if you adjust for the interval size, you'll see
(c) False. Examine the class intervals. While the percentages just about total 100%, the heights are draw incorrectly and are misleading.
Chapter 4 Review
1 (a) Average = 50 (sum of 41,48,50,50,54,57 divided by 6)
SD = square root of ( sum of the squared deviations / 6)
SD= square root of (81+ 4+0+0+16+ 49)/6 = 5
(b) 48,50,50 are within 0.5 SD of average (i.e. they fall within 47.5-52.5), 48,50,50,54,57 are within 1.5SD (i.e. they fall within 42.5 - 57.5)
4. Income -- average is bigger than median. (see p.64-65)
Education -- average is smaller than median (p.39)
6 (a) 60, 50 , 40
(b) (i) median is bigger than average
(ii) median is about equal to the average
(iii) median is less than the average
9.(a) False. For example a list like 1, 2, 99 has a median of 2 and an average of 34.
(b) False, for the list above, 2/3s of the entries are below the average.
(c) False. For example the income data on page 88 has a long right hand tail. Education has a long left hand tail with bumps at 8,12, and 16.
(d) False. If the histogram for a list follows the normal curve, the percentage within + or - 1 standard deviation will be around 68%, otherwise the percentage could be a lot different. Example, take 8 numbers, 30, 50 ,50,50,50,50,50, 70 the average is 50, the SD is 10, and 75% are within +/- one standard deviation.