Math Problem Statement

Given two dependent random samples with the following results:

Population 1

30

15

28

44

26

47

32

Population 2

44

28

36

35

18

35

22

Use this data to find the 95% confidence interval for the true difference between the population means. Assume that both populations are normally distributed.

Step 3 of 4 :  

Calculate the margin of error to be used in constructing the confidence interval. Round your answer to six decimal places.

Solution

To calculate the margin of error (ME) for the 95% confidence interval for the difference between the means of two dependent random samples, we proceed with the following steps:

Step 1: Compute the differences (did_i) between the paired values

Let di=Population 1 valuePopulation 2 valued_i = \text{Population 1 value} - \text{Population 2 value}.

[ d = [30-44, 15-28, 28-36, 44-35, 26-18, 47-35, 32-22] = [-14, -13, -8, 9, 8, 12, 10] ]

Step 2: Calculate the mean of the differences (dˉ\bar{d})

dˉ=din\bar{d} = \frac{\sum d_i}{n}

dˉ=14138+9+8+12+107=470.571429\bar{d} = \frac{-14 - 13 - 8 + 9 + 8 + 12 + 10}{7} = \frac{4}{7} \approx 0.571429

Step 3: Calculate the standard deviation of the differences (sds_d)

The formula for sds_d is:

sd=(didˉ)2n1s_d = \sqrt{\frac{\sum (d_i - \bar{d})^2}{n-1}}

First, calculate each (didˉ)2(d_i - \bar{d})^2: (140.571429)2=212.469388,(130.571429)2=179.755102,(80.571429)2=73.469388(-14 - 0.571429)^2 = 212.469388, \quad (-13 - 0.571429)^2 = 179.755102, \quad (-8 - 0.571429)^2 = 73.469388 (90.571429)2=70.612245,(80.571429)2=55.755102,(120.571429)2=129.183673,(100.571429)2=89.183673(9 - 0.571429)^2 = 70.612245, \quad (8 - 0.571429)^2 = 55.755102, \quad (12 - 0.571429)^2 = 129.183673, \quad (10 - 0.571429)^2 = 89.183673

Sum these values: (didˉ)2=212.469388+179.755102+73.469388+70.612245+55.755102+129.183673+89.183673=810.428571\sum (d_i - \bar{d})^2 = 212.469388 + 179.755102 + 73.469388 + 70.612245 + 55.755102 + 129.183673 + 89.183673 = 810.428571

Now calculate sds_d: sd=810.42857171=810.4285716=135.07142911.621158s_d = \sqrt{\frac{810.428571}{7-1}} = \sqrt{\frac{810.428571}{6}} = \sqrt{135.071429} \approx 11.621158

Step 4: Calculate the standard error of the mean difference (SEdSE_d)

The formula for SEdSE_d is: SEd=sdnSE_d = \frac{s_d}{\sqrt{n}}

SEd=11.621158711.6211582.6457514.389150SE_d = \frac{11.621158}{\sqrt{7}} \approx \frac{11.621158}{2.645751} \approx 4.389150

Step 5: Find the critical value for a 95% confidence level (tt^*)

For n1=71=6n-1 = 7-1 = 6 degrees of freedom and a 95% confidence level, the critical tt-value is approximately t=2.447t^* = 2.447 (from a tt-distribution table).

Step 6: Calculate the margin of error (ME)

The formula for MEME is: ME=tSEdME = t^* \cdot SE_d

ME=2.4474.38915010.739613ME = 2.447 \cdot 4.389150 \approx 10.739613

Final Answer:

The margin of error is: 10.739613\boxed{10.739613}

Let me know if you'd like further clarification or assistance with this problem. Here are five related questions to expand on this topic:

  1. How is the tt-value chosen for constructing the confidence interval?
  2. Why is the paired sample standard deviation used instead of individual standard deviations?
  3. What changes in the calculation if the samples were independent instead of paired?
  4. How does increasing the sample size affect the margin of error?
  5. Can the confidence interval be interpreted as a probability statement?

Tip: Always verify whether the assumptions (normality and paired data) are satisfied before using tt-distribution methods for confidence intervals.

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Math Problem Analysis

Mathematical Concepts

Confidence Interval
Paired Sample t-Test
Normal Distribution
Statistics

Formulas

Mean difference: \(\bar{d} = \frac{\sum d_i}{n}\)
Standard deviation of differences: \(s_d = \sqrt{\frac{\sum (d_i - \bar{d})^2}{n-1}}\)
Standard error: \(SE_d = \frac{s_d}{\sqrt{n}}\)
Margin of error: \(ME = t^* \cdot SE_d\)

Theorems

Central Limit Theorem
t-Distribution

Suitable Grade Level

Undergraduate - Introductory Statistics