CODEWITHSUNDEEP
excelexcel-formula
technogreen1
technogreen1

Reputation: 23

Apparent Confidence Interval Discrepancy in Excel

I would really appreciate your help with this discrepancy that I am not able to explain.

If I go about finding the 95% confidence interval of a set of data by first finding the standard deviation/mean, I am getting a different answer than if I use the Data Analysis Tool --> Descriptive Statistics --> Confidence Level.

For example, for the following data set (n = 16):

14, 9, 11, 9, 14, 10, 13, 14, 15, 13, 11, 11, 10, 14, 11, 13.

stdev = 1.966
average = 12 
count = 16

=confidence.norm(0.05,1.966,16) = **0.9635**

HOWEVER,

When this set of data is plugged into the "Descriptive Statistics" Tool, I receive a "Confidence Level (95.0%) = 1.0478"

Are these two things measuring separate variables that I am not noticing? How should I be interpreting this?

Thank you in advance!

Upvotes: 2

Views: 142

Answers (1)

JvdV
JvdV

Reputation: 75900

The discrepancy seems to be the result between the use of a t-distribution (Tool) instead of a normal distribution (Function). Instead try:

=CONFIDENCE.T(0.05,1.966,16)

That being said, 1.966 is not the true standard deviation either, but based on a sample set of data. I assume you either used STDEV.S() or STDEV(). Instead, if your data is not representing just a piece of sample data but rather your entire dataset, use STDEV.P().

Upvotes: 2

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