# How to Calculate Confidence Interval Proportion in Excel

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When you want to gather any formation based on a large population, things get difficult sometimes to capture this huge number of people. In that case, we tend to go for the confidence interval which is calculated for a small group of people, that represent the whole population. In Microsoft Excel, we can easily calculate the confidence interval based on their proportion. Therefore, in this article, we will guide you on how to calculate confidence interval proportion in excel with 2 useful examples.

Get this sample file to try the process by yourself.

## What Is Confidence Interval?

Before starting the calculation, we must understand the confidence interval first. According to statistics, it is basically a probability of a specific parameter that falls between a couple of values. Confidence interval measures the level of certainty of uncertainty in a trial process.

Now, in the case of proportion, the confidence interval provides a range of values that contains a proportion of the population with a level of confidence in a specific sample test. The values show the confidence interval proportion for both high and low estimations.

## Mathematical Formula of Confidence Interval for Proportion

To calculate the confidence interval for proportion, we have to use this formula.

Confidence Interval = pÂ  +/-Â  z*âˆšp(1-p) / n

Here,

p = Proportion of Success

z = Chosen z-Value

n = Sample Size

In the formula, the z-value is dependent on the confidence level which generally differs from 90% to 99%. Moreover, the relationship between the z-value and the confidence interval is always proportional. The confidence interval for proportion is always calculated for both the upper and lower bound.

## 2 Useful Examples of Calculating Confidence Interval for Proportion in Excel

Finally, we will start calculating the confidence interval for proportion with 2 examples. Here, we will do the calculation with the mathematical formula that we described above. Along with it, we will also apply the Excel formula for the calculation. So, without further delay, letâ€™s go through the calculation.

### Example 1: Find Confidence Interval Proportion with Excel Formula

To illustrate the process, let us assume we have run a survey on 100 students to find out the proportion of their acceptance of the new curriculum. Seems like, out of 100, 56 students have agreed on the new curriculum with a confidence level of 95%. Now, taking these parameters, let us find out the confidence interval for the proportion of this case.

• In the beginning, insert the values of Sample Size, Number of Confidence Levels and rate of Confidence Level in the cell range C5:C7.

• Then, calculate the Proportion of Success with this formula in cell C8 and press Enter.
`=C6/C5`

• Along with it, find out the Proportion of Failure as well in cell C9.
• For this, type this formula and hit Enter.
`=1-C8`

• Now, calculate the Alpha value based on the Confidence Level with this formula in cell C10.
`=1-C7`
• Following, press Enter.

`=ABS(NORM.S.INV((C10)/2))`

Here, the NORM.S.INV function is used to return the inverse value of cell C10. along with it, we attached the ABS function to get an absolute value.
• Lastly, insert this formula to get the Margin of Error for proportion in cell C12.
`=C11*SQRT(C8*C9/C5)`

In this formula, the SQRT function is used to square root the output of calculation between cells C8, C9 and C5.
• Lately, hit Enter and you will get all the parameters that we will need for the final calculation.

• Now, type this formula in cell C14 to calculate the Upper Bound.
`=C8+C12`

• Also, apply this formula for calculating Lower Bound in cell C15.
`=C8-C12`

• Finally, hit Enter.
• Thatâ€™s it, you can now see the true proportion of the confidence interval based on the survey.

### Example 2: Calculate Confidence Interval Proportion with Mathematical Formula

In this section, we will take the same case scenario for calculation. The only difference is that we will find out the proportion of the confidence interval by calculating it with the mathematical formula. Letâ€™s see how it works.

• First, insert all the parameters up to z-Value in the cell range B5:C11 that we got from the example above.

• Now, insert this mathematical formula in cell C12 to calculate the Margin of Error.
`=C11*((C8*C9)/C5)^0.5`

• After this, hit Enter to get the output.

• Next, type this formula in cell C14 to calculate Upper Bound.
`=C8+C12`

• Lastly, get the Lower Bound value in cell C15 with this formula.
`=C8-C12`

• Finally, hit Enter.
• Thatâ€™s it, you can see that the true proportion values of confidence intervals are the same for any type of formula.

## How to Calculate Confidence Interval for Difference in Proportion in Excel

So far, we calculated the confidence interval for a single bunch of students. Let us consider now two groups of students where each group has 100 people. But the confidence levels are 56 and 46 respectively. The basic formula to calculate the difference is as follows,

Confidence interval = (p1â€“p2)Â  +/-Â  z*âˆš(p1(1-p1)/n1 + p2(1-p2)/n2)

Where,

p1, p2 = Proportion of sample 1 and sample 2

n1, n2 = Sample size of sample 1 and sample 2

Now, we will calculate the confidence interval for the difference in proportion among these two groups for a confidence level rate of 95%.

• First, insert all the parameters for each group in the cell range B5:E12.

• Then, type this formula in cell C14 to get the difference in Upper Bound.
`=(C8-E8)+(C12+E12)`

• Press Enter.
• Lastly, insert this formula to calculate the difference of proportion in the Lower Bound in cell C15.
`=(C8-E8)-(C12+E12)`

• Finally, hit Enter.
• Thatâ€™s it, you will get the difference in proportion between the two groupsâ€™ acceptance of the new curriculum.

## Conclusion

Concluding the article, I hope that you have got a clear understanding of how to calculate confidence interval proportion in excel with 2 useful examples. Let us know your insightful suggestion in the comment box. Keep learning Excel with ExcelDemy.

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#### Sanjida Mehrun Guria

Hello! Welcome to my blog. I have completed my Bachelor in Architecture from Ashanullah University of Science & Technology, Dhaka. I am a passionate, goal-oriented person with an immense thirst for knowledge and an attitude to grow continuously. Besides Architectural work, I find it very enthusiastic to work in Excel blogging. Exceldemy is a platform where I have got the opportunity to flourish my skill in Microsoft Excel and therefore, here I will be posting blogs related to it.

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