Excel Guide
Chapter 7
Chapter 7 – Confidence Intervals
Excel does not have an automated function to calculate Confidence Intervals. For Confidence
Intervals for Mean and Proportions, use MEGASTAT: MEGASTAT Confidence Intervals /
Sample Size.
Fig 7-1
This input screen has 5 tabs to select the type of computation you need to perform.
A.
B.
C.
D.
E.
Confidence interval – mean
Confidence interval – p
Sample size – mean
Sample size – (alpha, beta)
Sample size – p
: for the Mean (Both z and t Distributions)
: for Proportions
: for the mean
: OMIT
: for Proportions
For Confidence Interval for Variance / Standard Deviations use MEGASTAT:
MEGASTAT Hypothesis Tests Chi-square variance test
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Chapter 7
A. Confidence Interval – mean
Examples
Section 7-3: Exercise 6, Page 362:
1. Enter the data into a spreadsheet or find the data set P-C07-S03-6.xls in your data disk
and open it.
Fig 7-2
2. Calculate the average sales tax (Cell B2) : =Round(Average(A2:A18),1) = 91.1 and the
Sample Standard Deviation (Cell C2): =Round(Sdev(A2:A18),3) = 38.366
3. MEGASTAT Confidence Intervals / Sample Size, Click on Confidence Interval - mean,
and input the values for Mean, Std. Dev., and n.
Choose the “t radio button” ( σ not known and n < 30). Then type 98 in the Confidence
Level box and click on the Preview button to see the calculated Confidence Interval:
67< µ <115.1 If you press ok, Megastat will place the assumptions and calculated values
on a new sheet in the existing workbook, called “Output”
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Chapter 7
Fig 7-3
NOTE: If σ were known or n ≥ 30, then you would click on the “z radio button”
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Chapter 7
Section 7-3: Exercise 7, Page 362:
1. Enter the data into a spreadsheet or find the data set P-C07-S03-7.xls in your data disk
and open it.
Fig 7-4
2. Calculate the sample mean and sample standard deviation as above.
3. Input the data; make sure to click on the “t radio button” and set the Confidence Level to
90%. The Preview area shows the calculated Confidence Interval. Point Estimate of the
population mean is the sample mean of 33.4
Section 7-3: Exercise 8, Page 362:
Enter the data into a spreadsheet or find the data set P-C07-S03-8.xls in your data disk and
open it. Follow procedure as above.
Section 7-3: Exercise 10, Page 362:
Enter the data into a spreadsheet or find the data set P-C07-S03-10.xls in your data disk and
open it. Follow procedure as above.
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Chapter 7
B. Confidence Interval – p (Proportion)
Section 3-4: Exercise 4, Page 370
MEGASTAT Confidence Intervals / Sample Size, Click on Confidence interval – p:
Fig 7-5
Enter the proportion and sample size. (as you can see, you can enter the proportion either
as a fraction or as a decimal).
Enter the required Confidence Level and click on the Preview button to see the result.
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Chapter 7
C. Sample size – mean
Section 7-2: Exercise 24, Page 355
MEGASTAT Confidence Intervals / Sample Size, Click on Sample size – mean:
Fig 7-6
Enter the Error value and Standard deviation. Choose the Confidence level and click on
Preview to see the result.
E. Sample size – p (Proportion)
Section 7-3: Exercise 19, Page 371
MEGASTAT Confidence Intervals / Sample Size, Click on Sample size – p:
Fig 7-7
Enter the value for Error and the population proportion (If not known, enter 0.5); Choose the
Confidence level and click on Preview to see the results.
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Chapter 7
F. Confidence Interval for Variance
Use MEGASTAT Hypothesis Tests Chi-square Variance test.
Section 7-5: Exercise 7, Page 378
Enter the data into a spreadsheet or find the data set P-C07-503-7.xls in your data disk and
open it
Enter the data range into the Input Range field.
Specify any value for “Hypothesized variance”
Select any value for “Alternative”
Select the required Confidence Level
Check the “Display” field.
Click on OK
Fig 7-8
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Chapter 7
The output is shown below:
Fig 7-9
NOTE: If you do not have the raw sample data, but instead you have the sample variance
and sample size, then you need to create a three cell area (as shown below) with a label in
row 1, the variance in row 2, and the sample size in row 3, and check the summary Input
radio bottom. Then input the spreadsheet range that contains these three values.
Fig 7-10
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Chapter 8
Hypothesis Testing.
Hypothesis (one or two means or proportions) is performed through
MEGASTAT Hypothesis Testing
and then choosing the appropriate submenu
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Chapter 10
Correlation and Regression
MEGASTAT Correlation / Regression Regression Analysis
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