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Question 1

Motor vehicles have a recommended tire pressure of 32 psi (pounds per square inch). The

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road safety authority launches a roadside checkpoint to measure the actual tire pressure in the

front left tire of a random sample of 50 passing cars. The authority hopes to use this

information to decide whether an additional investment in air pumps is required at filling

stations.

(a) Define the population characteristic of interest in the above example. (2 marks)

(b) The following SPSS output has been produced from a one sample t-test. Using the 5-step

approach to hypothesis testing, determine whether the road safety authority should invest in

additional air pumps at filling stations. (7 marks)

One-Sample Statistics

N Mean

Std.

Deviation Std. Error Mean

Tire pressure 50 32.8200 1.98659 .28095

One-Sample Test

Test Value = 32

t df

Sig.

(2-tailed)

Mean

Difference

95% Confidence Interval of

the Difference

Lower Upper

Tire pressure 2.919 49 .005 .82000 .2554 1.3846

(c) The following 95% confidence interval has been computed for the mean tire pressure of

all motor vehicles. Does the confidence interval support the conclusion you made in part (b)?

Explain your answer. (3 marks)

(d) Assume that the median tire pressure of all motor vehicles is 32.82. Produce an

appropriate graph that gives an approximation of the likely distribution of the tire pressure

variable. (3 marks)

(Note: You may use insert: shapes: lines: freeform scribble or manually sketch the graph and

insert a photographic image of the graph in your word solution document.)

(e) Redraw the graph assuming that the median tire pressure of all motor vehicles is actually

34. (3 marks)

(f) Comment on the graph in part (e) and provide an example of a dataset that would likely

follow a similar distribution. (2 marks)

Total 20 marks

95% Confidence

Interval for Mean

Lower Bound 32.2554

Upper Bound 33.3846

Question 2

Political science students at a university carry out a survey of 1,669 randomly selected

registered voters. They wish to determine if there is an association between the respondents’

political party (Republican or Democrat) and their opinion about a newly proposed gun

control law (support or oppose). The following two-way table summarizes the count data.

Gun control law

Total Support Oppose

Political

party

Democrat 438 247 685

Republican 374 610 984

Total 812 857 1669

(a) Among those who are democrats, what percentage supports the newly proposed law?

(1 mark)

(b) Among those who are republicans, what percentage supports the newly proposed law?

(1 mark)

(c) Do your calculations in parts (a) and (b) indicate that there is an observed relationship

between political party and opinion about the gun control law? Explain your answer.

(2 marks)

(d) Assuming that a relationship between the two variables is observed in the sample, can the

political science students infer from this that there is a relationship in the population?

If not, how would they go about making this inference? (4 marks)

The economic and social research institute has gathered data on the potential factors that

influence current salary levels in the market. The following statistical output has been

produced from a linear regression, with current salary as the response variable and education

(no. of years) and previous experience (no. of months) as the explanatory variables.

Coefficientsa

Model

Unstandardized

Coefficients

Standardized

Coefficients

t Sig. B Std. Error Beta

1 (Constant) -20978.304 3087.258 -6.795 .000

Education 4020.343 210.650 .679 19.085 .000

Previous experience 12.071 5.810 .074 2.078 .038 a. Dependent Variable: Current salary

(e) Does an individual’s education predict their current salary well? Explain your answer with

specific reference to the beta coefficient of 4020.343. (4 marks)

(f) Provide an example of a possible confounding variable that might change your

interpretation in part (e). Explain your answer. (4 marks)

(g) What would influence your conclusion on whether an individual’s previous experience is

significantly related to their current salary? (4 marks)

Total 20 marks

Question 3

The department of health is currently drafting a new health initiative to promote weekly

exercise. The department wants to identify which groups in society most need additional

supports to increase their amount of weekly exercise. The department issues a survey to a

random sample of 100 employed individuals asking them “How many minutes do you

typically exercise in a week?” The summary statistics from the sample are:

Society group N Mean Standard

deviation

Employed in low income job

55 180.63 33.65

Employed in high income job

45 201.08 44.23

(a) Suggest an appropriate statistical test that would provide useful information to allow the

department to identify where supports are most needed in the population.

Explain your answer. (3 marks)

(b) Assuming a p-value of 0.073, write out the approach to the statistical test you suggested in

part (a). Clearly state your conclusion.

(4 marks)

(c) Based on your conclusion in part (b), what recommendation would you make to the

department of health regarding which group most needs additional supports to increase their

amount of weekly exercise. (2 marks)

(d)

Assume that the department of health gathers additional data on the minutes of weekly

exercise from a third group in society:

Society group N Mean Standard

deviation

Unemployed

47 111.35 18.79

Suggest an appropriate statistical test that would allow for this additional data to be

incorporated into the previous analysis. (2 marks)

(e) Assume that the distribution of weekly exercise in minutes is bell-shaped. Using the

Empirical Rule, explain whether or not it would be unusual for an unemployed individual to

exercise for the same amount of time as an average individual employed in a high income

job.

(4 marks)

Total 15 marks

Question 4

Bailey Office Ltd. sells office supplies including a popular printer refill ink. Weekly demand

for the ink is normally distributed with a mean of 60 litres and a standard deviation of 24

litres. When the stock of this ink drops to 80 litres, Bailey Office Ltd places a replenishment

order. The delivery from the supplier takes place within one week of the order being placed.

The store manager is concerned that sales are being lost due to stockouts while waiting for

orders to be delivered.

(a) What is the probability of a stockout occurring? Explain in detail your approach to

calculating the probability. (5 marks)

(b) If the store manager wants the probability of a stockout to be no more than 5%, at what

level of stock should he place the replenishment order? (3 marks)

(c) Provide a brief personal reflection on how this module has helped you to both analyse

quantitative data and to interpret and present results from such analyses. (7 marks)

Total 15 marks

END

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