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95% confidence interval for mean differences

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What would be the 95% confidence interval for this difference?

95% CI = mean difference +/- 2(standard error of the difference)

t = 5.185
df = 13201
mean dif = -.16
Std. Error Dif = .031
95% CI (lower -.221)
(upper -.100)

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Solution Preview

Let's take a closer look. First, this response points out how the computer print-out gives you the confidence interval and then we manually calculate the interval to see how the computer used this formulas to get the upper and lower levels of the 95% confident interval.

RESPONSE:

95% CI = mean difference +/- 2(standard error of the difference)

t = 5.185
df = 13201
mean dif = -.16
Std. Error Dif = .031 ...

Solution Summary

This solution addresses the question: What would be the 95% confidence interval for this difference?

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Confidence Interval-difference between means (small sample)

The university data center has two main computers. The center wants to examine whether computer 1 is receiving tasks that require processing times comparable to those of computer 2. A random sample of 10 processing times from computer 1 showed a mean of 69 seconds with a standard deviation of 15 seconds, while a random sample of 11 processing times from computer 2 (chosen independently of those for computer 1) showed a mean of 67 seconds with a standard deviation of 17 seconds. Assume that the populations of processing times are normally distributed for each of the two computers and that the variances are equal. Construct a 95%confidence interval for the difference M1-M2 between the mean processing time of computer 1,M1 , and the mean processing time of computer 2, M2. Then complete the table below.

Answer to 3 decimal places

1. What is the lower limit of 95% confidence interval?

2. What is the upper limit of 95% confidence interval?

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