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Unformatted text preview: we Midterm 1. California is evaluating a new program to rehabilitate prisoners before their release. The object
is to reduce the “recidivism rate” 7 the percentage who will be back in prison within two years
of release. The program involves several months of “boot camp” — a military—style basic training
with very strict discipline. Admission to the program is voluntary. It was found that inmates
who completed boot camp were less likely to return to prison than other inmates. (2) (a) What is the treatment group? What is the control group? (3) (b) Is this an observational study or a randomized experiment? Explain your answer. (5) {(3) True or false: the data show that the boot camp reduced recidivism. Explain brieﬂy. (3} (3) (3) Midterm 2. In each of the following statements, circle any and all options that apply (so you can circle
more than one). You do NOT need to explain your choices. (a) The following methods are probability sampling methods:
simple random sampling / convenience sampling / quota sampling / cluster sampling (b) A histogram always balances when supported at its:
average / median / standard deviation / 75th percentile / none of these (c) When the r.m.s. size of a list is zero, then all entries must be:
equal to each other / equal to zero / none of these (d) When all entries in a list are multiplied by 2, which of the following change?
average / median / standard deviation / standard units / none of these (e) When a constant is added to all entries in a list, which of the following change?
average / median / standard deviation / standard units / none of these Midterm 3. A study of 500 babies looked at their weight at birth. The birth weights averaged out to 107
ounces with an SD of 15 ounces. The histogram of the weights follows the normal curve. (4) (a) A baby is said to have low birth weight if his/ her weight is below 88 ounces. Estimate the
percentage of babies with low birth weight. Midterm (4) (b) Estimate the 85th percentile of the birth weights. (5) (10) 5. The following data set is given: wHUerbJb
ﬂmmHMh Moreover, the following information is given: 3
4 Average of x
Average of y
SD of y = 2 (a) Compute the SD of 3:. (b) Compute the correlation coefficient r. (5) Midterm 5. A statistical analysis was made of the midterm and ﬁnal scores in a large course, with the
following results: 25,
15, Midterm score: Average 65, SD
Final score: Average = 60, SD
r = 0.6 The scatter diagram was football—shaped. For each student, the ﬁnal score was predicted from
the midterm score using the regression line. (a) For about 1/3 of the students, the prediction for the ﬁnal score was off by more than .....
points. Fill in the blank. Options: 6, 9, 12, 15, 16, 20, 25. Explain your choice. (b) Predict the ﬁnal score for a student whose midterm score was 80. This question continues on the next page. Midterm (5) (c) The prediction of part (b) is likely to be off by ..... points or so. Fill in the blank. Options:
6, 9, 12, 15, 15, 20, 25. Explain your choice. (5) (d) Of the students who scored 80 on the midterm, about what percentage scored over 80 on
the ﬁnal? ...
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 Spring '08
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