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How to Calculate Confidence Interval for Slope in Excel

We can perform many extensive statistical calculations with Excel easily. The confidence interval is one of the most important calculations in statistics. This can be calculated through data and also through the slope of a dataset. In this article, I will show you all the steps to calculate the confidence interval for slope in Excel.


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Steps to Calculate Confidence Interval for Slope in Excel

Say, we have a dataset of 10 pairs of x and y values. From these data, we will easily get a slope. And, now we have to calculate the confidence interval for that slope. Follow the step-by-step guidelines below to accomplish your desired result.

Sample Dataset to Calculate Confidence Interval for Slope in Excel


📌 Step 1: Calculate Standard Error in Slope

First and foremost, you will need to calculate the standard error in slope to calculate the confidence interval for slope in Excel.

  • To do this, click on cell F5 and insert the SLOPE function formula below.
=SLOPE(C5:C14,B5:B14)
  • Subsequently, press the Enter key.

Insert SLOPE Function to Get Slope

  • Now, you will need to calculate the standard error for slope using the INDEX and LINEST functions.
  • In order to do this, click on cell F6 and insert the following formula.
=INDEX(LINEST(C5:C14,B5:B14,1,1),2,1)
  • Subsequently, hit the Enter key.

Calculate the Standard Error for Slope to Calculate Confidence Interval for Slope in Excel

Read More: How to Find Uncertainty of Slope in Excel (with Easy Steps)


📌 Step 2: Calculate the Multiplier T Value

Now, you will need to calculate the multiplier, T value for calculating the confidence interval for the slope.

  • To do this, first, click on cell F7 and insert the following formula which includes the COUNT function to find the degrees of freedom.
=COUNT(B5:B14)-2
  • Subsequently, hit the Enter key.

Calculate the Degrees of Freedom to Calculate the Confidence Interval for Slope in Excel

  • Afterward, click on cell C8 and insert your desired confidence level.

Insert Confidence Level to Calculate Confidence Interval for Slope in Excel

  • Now, you have to use the TINV function to calculate the multiplier, T.
  • To do this, click on cell F9 and insert the formula below.
=TINV((1-F8),F7)
  • Subsequently, press the Enter key.

Calculating T Value to Calculate Confidence Interval for Slope in Excel

Read More: How to Calculate Slope and Intercept in Excel (3 Easy Methods)


Similar Readings


📌 Step 3: Calculate Confidence Interval for Following Slope

Last but not least, you will have to now calculate the confidence interval.

  • For doing this, click on cell F10 and insert the formula below.
=F9*F6
  • Subsequently, press the Enter key.

Calculating Confidence Interval for Slope in Excel

  • Now, to get the slope with the confidence interval, click on cell F11 and insert the formula below including the ROUND function.
=ROUND(F5,3)&" ± "&ROUND(F10,3)
  • Subsequently, press the Enter key.

Slope Value with Confidence Interval in Excel

  • Afterward, to get the lower slope value with the confidence interval, click on cell F12 and insert the formula below.
=F5-F10
  • Subsequently, hit the Enter key.

Lower Slope Value with Confidence Interval in Excel

  • Similarly, to get the upper slope value, click on cell F13 and insert the formula below.
=F5+F10
  • Subsequently, press the Enter key.

Upper Slope Value with Confidence Interval in Excel

Thus, your whole calculation is done now. And, the final outcome would look like this.

Whole Summary for Calculating Confidence Interval for Slope in Excel

Read More: How to Find the Slope of a Line in Excel (5 Easy Ways)


How to Find Confidence Interval for Two Samples in Excel

Sometimes, it might happen that you have two sample values for something. And, now you will have to find the confidence interval from these values.

Say, you are given data on delivery time for two delivery service companies. Now, you need to calculate the confidence interval for these values. You can use the CONFIDENCE function to accomplish this. Follow the steps below to achieve this result.

Sample Dataset to Calculate Confidence Interval for Two Samples in Excel

📌 Steps:

  • First and foremost, click on cell C9 and insert the following formula including the AVERAGE function to get the mean.
=AVERAGE(D5:D6)
  • Following, hit the Enter key.

Calculating Mean

  • Now, to get the standard deviation, you have to use the STDEV.S function.
  • To accomplish this, click on cell C10 and insert the following formula.
=STDEV.S(D5:D6)
  • Subsequently, hit the Enter key.

Calculating Standard Deviation

  • Afterward, click on cell C11 and insert your desired confidence level.

Insert the Confidence Level

  • Afterward, click on cell C12 and insert the formula to find the significance level (Alpha).
=1-C11

Calculate the Significance Level

  • At this time, click on cell C13 and insert the sample size.

Insert the Sample Size

=CONFIDENCE.NORM(C12,C10,C13)

Calculating Confidence Interval for Two Samples

  • Now, click on cell C15 and insert the following formula with the TEXT function to get your final outcome of mean with confidence interval.
=C9&" ± "&TEXT(C14,"##.##")
  • Subsequently, hit the Enter key.

Calculating Confidence Interval for Two Samples

As a result, you will get the whole output you desired. And, the outcome should look like this.

Whole Summary for Calculating Confidence Interval for Two Samples


Conclusion

So, in this article, I have shown you all the steps to calculate the confidence interval for slope in Excel. You can also download our free workbook to practice. I hope you find this article helpful and informative. If you have any further queries or recommendations, please feel free to comment here.

And, visit ExcelDemy to learn more things about Excel! Have a nice day! Thank you!


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Tanjim Reza

Tanjim Reza

Hello! I am Md. Tanjim Reza Tanim. I have just completed my B.Sc from Naval Architecture & Marine Engineering Department, BUET. Currently, I am working as an Excel & VBA content developer. I always had a great fascination with Microsoft Excel and its cool functions and formulas. Here, I am learning every day about new functions and formulas and working on applying MS Excel to the analysis of our real-life problems. I have great enthusiasm for learning any kind of new things, writing articles, and solving real-life problems.

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