Social Studies 201 – Winter, 2001

Second Midterm Examination – 1:30 to 2:20 p.m., March 19, 2001

Answer any three (3) questions.  Each question has equal value.

 

1.      Probabilities. 

 

a. For each of the two quotes below, explain which concepts of probability (theoretical, frequency, subjective) appear to be used in the word in bold letters.

b. In the second quote concerning job outlook, identify a pair of events that is either independent or dependent, and explain why they have this characteristic.

 

In a report on the possibility of faulty hospital tests,

Montreal radiologist Dr. Gaetan Barrette said he experienced the problem first-hand when he told a patient the ultrasound machine he was using in a remote part of Quebec was so unreliable that if the patient had liver cancer, there was only a 50 per cent chance of finding it.  (The Globe and Mail, March 17, 2001, p. A1).

 

A recent article, “Arts Grads Face Tough Job Outlook” notes:

The adage that it pays to get an education doesn’t apply to arts and culture graduates, according to a new Statistics Canada study, which suggests that for them Canada is a wasteland.

Compared with other graduates, the federal agency says “arts and culture graduates were more likely to be moonlighting, be self-employed, earn lower pay, change employers, and find only temporary work. (National Post, March 17, 2001, p. A10).

 

 

2. Binomial and normal approximation to the binomial.  

 

In the Saskatchewan provincial election of September 16, 1999, there were 58 seats of the Legislative Assembly to be decided.  The NDP obtained 29 seats, the Saskatchewan Party obtained 26, the Liberals obtained 3, and other parties received none.   The distribution of popular vote among the parties is shown in Table 1.  Use the binomial distribution, with probability of success being the proportion of the popular vote, to obtain the following.

a. Using the distributions in Table 2, what is the probability that the Saskatchewan Party would obtain at least 26 seats but less than 30 seats?

b. Use the normal approximation to the binomial to determine the probability that the NDP would obtain exactly 29 seats. 

c. Cite any reasons why the probability in b. might not represent the chance that the NDP would win exactly 29 seats.

 

 


3. Probabilities from a cross-classification table.   Use Table 3.

 

The data in Table 3 concern the issue of whether there is a connection between homicide offenders and victims.  The author, Wendy C. Regoeczi, examines this issue by looking at the previous conviction record of both offenders and victims and cross-classifying these.  The categories are identified by letters from A to F.

 

a.  The author notes that the proportion of victims “with previous criminal records is relatively small” (p. 498).  Obtain a probability that demonstrates this.

b. What is the conditional probability of selecting a victim with a violent conviction (E) given that the offender has no record (A).

c. Is the event of a victim having a violent conviction independent of the event of the offender having no record?

d. Is the event of a victim having a violent conviction close to independent of the event of an offender having a violent conviction?

e. From c. and d. comment on the author’s statement that “these findings provide a relatively weak support for the hypothesis that there is a link between victimization and offending” (p. 499).

 

 

4. Normal distribution.   

 

a. As noted in Table 5, the mean minutes of media use daily for Saskatchewan adults is 207 and the standard deviation is 162 minutes daily.  Assuming that use of the media is a normally distributed variable, obtain the following:

i. The proportion of adults who use the media more than 240 minutes daily.

ii. The probability that a randomly selected Saskatchewan adults uses the media between 120 and 180 minutes daily.

iii. If a sample of 631 Saskatchewan adults is selected randomly, how many would be expected to use the media less than 1 hour daily?

b. Compare the results of a. with the numbers or percentages in Table 4.  Explain whether or not daily media use appears to be a normally distributed variable.

 

 

5. Interval Estimates.  Use Table 5.

 

a. Obtain 90% interval estimates for the true mean minutes of media use daily by those aged 15-24 and by those aged 55-64.  From these, does it seem likely that 55-64 year olds use the media more than do 15-24 year olds?

b. Using the data in the last row of Table 5, obtain a 99% interval estimate for the true mean media use daily for all Saskatchewan adults.  Explain why the width of this interval differs from the width of the intervals in a.


 

Table 3.  Number of offenders and victims of homicide among those aged 12-17, Canada, 1991 to 1995.

 

 

Victim’s Criminal Record

Total

None (D)

Violent Conviction (E)

Other Conviction (F)

Offender’s Criminal Record

None (A)

51

4

7

62

Violent Conviction (B)

25

5

12

42

Other Conviction (C)

19

5

17

41

Total

95

14

36

145

 

Source: Wendy C. Regoeczi, “Adolescent violent victimization and offending: Assessing the extent of the link,” Canadian Journal of Criminology, October, 2000, p. 500.

 

Table 4.  Distribution of time spent daily by Saskatchewan respondents using media.

 

Minutes per day

Number of Respondents

Per Cent of Respondents

0-60

99

15.7

60-120

121

19.1

120-180

110

17.4

180-240

77

12.2

240-300

67

10.6

300-360

59

9.4

360-420

32

5.1

420 plus

66

10.5

Total

631

100.0

 

Table 5.   Sample sizes, means, and standard deviations of minutes spent daily using media by Saskatchewan respondents of various ages.

 

Age

Sample Size

Mean Minutes Daily

Standard Deviation of Minutes Daily

15-24

80

168

128

25-34

113

154

123

35-44

115

180

137

45-54

84

179

133

55-64

88

202

160

65-74

81

280

183

75-84

51

336

195

85+

19

334

239

Total

631

207

162

 

Source for Tables 4 and 5.  Statistics Canada, General Social Survey, Cycle 12: Time Use, 1998.

 

 

 

Table 1.  Popular Vote by Party, Saskatchewan Election, 1999.

 

Party

Per Cent of Popular Vote

NDP

38.7%

Saskatchewan  Party

39.6%

Liberal Party

20.2%

New Green Alliance

1.5%

 

 

Table 2.  Binomial probability distributions.

 

n=58 p=0.387

n=58 p=0.396

n=58 p=0.202

n=58 p=0.0152

 

K    P( X = K)

8    0.0000

9    0.0001

10    0.0002

11    0.0007

12    0.0017

13    0.0038

14    0.0076

15    0.0141

16    0.0240

17    0.0374

18    0.0538

19    0.0714

20    0.0880

21    0.1005

22    0.1067

23    0.1054

24    0.0971

25    0.0833

26    0.0668

27    0.0500

28    0.0349

29    0.0228

30    0.0139

31    0.0079

32    0.0042

33    0.0021

34    0.0010

35    0.0004

36    0.0002

37    0.0001

38    0.0000

 

 

K    P( X = K)

9    0.0000

10    0.0002

11    0.0004

12    0.0011

13    0.0026

14    0.0055

15    0.0106

16    0.0186

17    0.0301

18    0.0450

19    0.0621

20    0.0794

21    0.0942

22    0.1039

23    0.1066

24    0.1019

25    0.0909

26    0.0756

27    0.0588

28    0.0427

29    0.0289

30    0.0183

31    0.0109

32    0.0060

33    0.0031

34    0.0015

35    0.0007

36    0.0003

37    0.0001

38    0.0000

 

 

K   P( X = K)

1    0.0000

2    0.0002

3    0.0010

4    0.0036

5    0.0099

6    0.0221

7    0.0415

8    0.0669

9    0.0941

10    0.1167

11    0.1289

12    0.1278

13    0.1145

14    0.0932

15    0.0692

16    0.0471

17    0.0294

18    0.0170

19    0.0090

20    0.0045

21    0.0020

22    0.0009

23    0.0003

24    0.0001

25    0.0000

 

 

K   P( X = K)

0    0.4113

1    0.3682

2    0.1620

3    0.0467

4    0.0099

5    0.0017

6    0.0002

7    0.0000