Calculate confidence

[wpryan]

Hi All, I inherited a power point presentation that shows the average, minimum and maximum values from survey response question. I have the underlying Excel data but don't have the work of the person that calculated these things. The average is shown, including the confidence level. I'm not a statistician and never took any courses on statistics. There were some errors to the survey responses that I must correct and update the presentation. I have done some searches about calculating confidence levels, and the calculated result is different than what shows on the presentation. This makes me wonder 1/is it really the confidence level calculated and shown on the presentation, or something else? or 2/ am I calculating it wrong? One sample
Numbers to be calculated:
30
0
20
15
5
90
30
50
50
5
5
5

The numbers shown on the presentation are 23.9 +/-25.2%. I am unsure how this number is calculated.

...any help? Thanks in advance.

 

[anglais428]

Do the numbers 23.9 +/- 25.2% relate directly to the numbers you have listed? As the average of these numbers is 25.42

 

[wpryan]

Hello, yes the number 23.9 comes directly from the presentation, based on the Excel table. I was also curious about that...

 

[anglais428]

It's difficult to see where that number is coming from.

 

[wpryan]

Yes I know. It seems to be an error. However, if I wanted to correct the info, could you point me to a resource how to calculate the confidence level? Thanks in advance.

 

[AhoyNC]

Maybe these links will be of some help.
https://www.youtube.com/watch?v=pJxNffzw3FI

http://www.statisticshowto.com/confidence-level/
https://www.khanacademy.org/math/statistics-probability/confidence-intervals-one-sample