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Week+7_Practice_problems

# Week+7_Practice_problems - Practice Problems Week 7...

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Practice Problems Week 7 Chi-square problems Question 1 The manager of an insurance company’s 24 hours emergency help line wishes to understand whether responsiveness to customer calls varies according to the time of day. The manager takes a random sample of 90 customer calls, and for each call determines the work shift during which the call was made, and whether the call was answered within 10 seconds. The data appears in the table below. Observed Work Shift Morning Mid-day Afternoon Night Graveyard Total Responsivenes s 5:00 - 10:00 10:00 - 14:00 14:00 -19:00 19:00 - 00:00 0:00 - 5:00 Answered in 10 seconds 19 14 12 10 4 59 Not Answered in 10 seconds 4 15 8 3 1 31 Total 23 29 20 13 5 90 a) Being careful to state your conclusions, and using a level of significance of = 5%, test whether responsiveness is independent of work shift. b) Using this question to provide examples, explain the difference between a type 1 and type 2 error.

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Question 2 When a customer moves out of a building, the phone lines are usually left intact by the phone company, ready to be activated when the next customer moves in. Usually these activations are effective but sometimes they are not. If the new customer has to report a fault within seven days of having a phone service activated, the activation is considered ineffective. The Operations Manager of telephone company is keen to better understand why some activations are ineffective. Some technicians have suggested that one factor might amount of time that service was inactive – that is, the number days between the previous customer leaving and the new customer wanting the service activated. To investigate these suggestions, the Operations Manager draws a random sample of 191 recent activations. For each activation, records are interrogated to find out how long the phone service was inactive and whether or not the new customer reported a fault within seven days of the activation. The data is summarised in the table below.
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• Spring '14
• Garofalo,LB
• Variance, Statistical hypothesis testing, Randomness, Statistical significance, SMAC, age based market

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