## How to Calculate Confidence Interval for the Mean: Excel

A confidence interval for the mean is a way of estimating the true population mean. Instead of a single number for the mean, a confidence interval gives you a lower estimate and an upper estimate. For example, instead of “6″ as the mean you might get {5,7}, where 5 is the lower estimate and 7 is the upper. The narrower the estimate, the more precise your estimate is. The equations involved in statistics often involve a lot of minor calculations (such as summation), plus you would also need to calculate the margin of error and the mean of the sample. It’s very easy for errors to slip in if you calculate the confidence interval by hand. However, Excel can calculate the mean of the sample, the margin or error and confidence interval for the mean for you. All you have to do is provide the data — which for this technique must be a sample greater than about 30 to give an accurate confidence interval for the mean.

Calculate Confidence Interval for the Mean: Excel

Sample problem:Calculate the 95 percent confidence interval for the mean in Excel using the following sample: 2,5,78,45,69,100,34,486,34,36,85,37,37,84,94,100,567,436,374,373,664,45,68,35,56,67,87,101,356,56,31

Step 1: Type your data into a single column in Excel. For this example, type the data into cells A1:A31.
Step 2: Click the “Data” tab, then click “Data Analysis” and then click “Descriptive Statistics.”
Step 3: Enter your input range into the Input Range box. For this example, your input range is “A1:A31″.
Step 4: Type an output range into the Output Range box. This is where you want your answer to appear. For example, type “B1.”
Step 5: Click the “Summary Statistics” check box and then place your chosen confidence level into the ‘Confidence Level for Mean’ check box. For this example, type “95″.
Step 5: Click “OK.”Microsoft Excel will return the confidence interval for the mean and the margin of error for your data. For this sample, the mean (Xbar) is 149.742 and the margin of error is 66.9367. So the mean has a lower limit of 149.742-66.936 and an upper limit of 149.742+66.936.

If the Data Analysis option isn’t in the data tab, make sure you have installed the Data Analysis Toolpak.
Warning: A 99 percent confidence interval doesn’t mean that there’s a 99 percent probability that the calculated interval has the actual mean. Your sample is either going to contain the actual mean, or it isn’t. Over the long-term, if you ran tests on many, many samples, there is a 99 percent probability that the calculated intervals would contain the true mean.

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## One Response to “How to Calculate Confidence Interval for the Mean: Excel”

1. ### Microsoft Excel for Statistics | said:

Jan 25, 13 at 8:52 am

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