28 Nov 2022

56

How to Calculate a Confidence Interval

Format: APA

Academic level: Master’s

Paper type: Coursework

Words: 410

Pages: 2

Downloads: 0

Question 1. Highest Mean Salary 

The position with the highest mean salary was the QB position, which had a mean salary of 4.041e+6.

Figure 1 

M  ean Salaries 

Question 2. Sampling 

The sample selected was 300, as it represented 15% of the total population of 2000. The mean of the population was 1.789e+6 and a standard deviation of 2.228e+6.

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Table 1 

Descriptive Statistics 

 

Total Salary 

Valid   

300 

 
Missing   

 
Mean   

1.789e +6 

 
Std. Deviation   

2.228e +6 

 
Minimum   

310000.000 

 
Maximum   

1.401e +7 

 
 

The sample size is adequate as it represented a significant percentage of the population. Smaller sample size would have increased the error in the result. The sampling method was appropriate as it was truly random. The function “Rand ()” identified random data from the sample and did not introduce any bias. The mean salary for players was determined as $1,789,000. The implication is that players, agents, teams should consider this as the average salary. The amount will be critical when negotiating about player earnings.

Task 2 Calculating Confidence Intervals 

1. Current Donation Level Amount 

The mean for the annual contribution was 6,212.057, and it had a standard deviation of 29,657.971. The mean for lifetime contributions was 82,010.188, and the standard deviation was 434,046.645. The values were as shown in table 2.

Table 2 

Descriptive Statistics 

 

Contribute Annually 

Contribute Lifetime 

Valid   

597 

 

584 

 
Missing   

47 

 

60 

 
Mean   

6212.047 

 

82010.188 

 
Std. Deviation   

29657.971 

 

434046.645 

 
Minimum   

100.000 

 

50.000 

 
Maximum   

500000.000 

 

1.000e +7 

 
 

The formula for calculating the confidence interval is:

CI = ± z * ( σ / 

Where is the sample mean , z appropriate z-value from the normal distribution table, σ is the standard deviation, and n is the sample size. The z-value for a 95% confidence interval is 1.96. 

For the annual giving amount, 

x̅ = 6,212.057, z = 1.96, σ = 29,657.971, and n = 597. 

CI = 6,212.057 ± 1.96 * ( 29,657.971 / 

CI = 6,212.057 ± 2379.08 

Upper = 8591.137, lower = 3832.977 

Standard error (SE) = Upper limit – Lower Limit)/z value 

Z value is (3.92 for 95% CI) 

SE = (8591.137 - 3832.977)/3.92 = 1213.82 

SE = 1213.82 

For lifetime giving amount x̅ = 82,010.188 , z = 1.96, σ = 434,046.645, and n = 584. 

CI = 82,010.188 ± 1.96 * ( 434046.645/ 

CI = 82,010.188 ± 35203.51 

Upper = 117,213.698, Lower = 46,806.678 

SE = ( 82,010.188 - 46,806.678)/3.92 

SE = 8980.48 

2. Additional Comments 

The mean annual contribution was calculated as 6,212.057, and the highest amount could be 8591.137 with the lowest 3832.977. The executive management should consider the amount when considering the budget for future years. The mean lifetime contributions were 82010.188, and the highest amount could be 117,213.698 with the lowest amount being 46,806.678. The lifetime contributions were significantly high, and the management should consider this as loyalty points for players.

Distribution Method 

Table 4. 

Annual Contributions Estimated Parameters 

 

95% CI 

Parameter 

Estimate 

SE 

Lower 

Upper 

μ   

6212.130 

 

1210.791 

 

3839.022 

 

8585.237 

 
σ²   

8.781e +8 

 

5.074e +7 

 

7.787e +8 

 

9.776e +8 

 
 
Note.  Standard errors and confidence intervals were calculated using the delta method. 

Table 5. 

Lifetime Contributions Estimated Parameters 

 

95% CI 

Parameter 

Estimate 

SE 

Lower 

Upper 

μ   

82011.638 

 

1482.910 

 

79105.187 

 

84918.089 

 
σ²   

1.881e +11 

 

1.286e +9 

 

1.856e +11 

 

1.906e +11 

 
 
Note.  Standard errors and confidence intervals were calculated using the delta method. 

Comparison of Values 

Values from calculation were compared to that in the distribution method. The comparison was shown in table 6. 

Table 6. 

Calculation vs. Distribution Method 

  Calculation  Distribution Method 
Annual Contribution     
SE  1213.82  1210.791 
Lower  3832.977  3839.022 
Upper  8591.137  8585.237 
Lifetime Contribution     
SE  8980.48  1 , 482.910 
Lower  46,806.678  79 , 105.187 
Upper  117,213.698  84 , 918.089 

The confidence interval and standard error values were similar in the annual contributions but different in lifetime contributions. The difference in the values could have been due to the difference in the formula applied. 

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Reference

StudyBounty. (2023, September 15). How to Calculate a Confidence Interval.
https://studybounty.com/how-to-calculate-a-confidence-interval-coursework

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