# mean and standard deviation.

• Aug 1st 2012, 09:24 AM
cmml100
mean and standard deviation.
Just a really dumb question here. If I surveyed a group of 30 people and a get a mean age of 20 and a standard deviation of 15. What does that tell me?

I am guessing that it implies most of my participants range from age 5 to 35? And given that there are only 30 people, and the wide range, it is a bit pointless to look at the mean and standard deviation after all.

Am I correct in saying that?

Mandy
• Aug 1st 2012, 09:59 AM
richard1234
Re: mean and standard deviation.
Define "most."

And no, you can use the mean and standard deviation for statistical purposes.
• Aug 1st 2012, 10:35 AM
cmml100
Re: mean and standard deviation.
Funny you say that. Actually, I typed in "most" because I do not know how to define it other than reusing the word standard deviation which I do not really properly understand. Let me have a go.

I know with the mean, I can say something is within plus or minus range of one standard deviation. I also think that standard deviation is to do with spread or concentration of the data.

So, back to my hypothetical survey example, if I only have those descriptive statistics, would I be correct to infer that the probably people of age group is equally represented?
• Aug 1st 2012, 10:50 AM
richard1234
Re: mean and standard deviation.
Yes, standard deviation essentially tells you how spread apart your data is...that's how it's defined. Standard deviation - Wikipedia, the free encyclopedia

About the word "most," statistics often uses what is called confidence intervals. For example, given your sample data, you can establish a 90% or 95% confidence interval, that is, a range of values for which you are 90% or 95% sure about where the true mean age is. For example, your confidence interval could be (5,35) or (18.3, 21.7). Confidence intervals are found by using the sample data, as well as a standard deviation (if known).

Re-word your third sentence. It makes no sense.
• Aug 1st 2012, 11:10 AM
cmml100
Re: mean and standard deviation.
Ah. okay, I understand this now. I have totally forgotten about that confidence level thing. thanks a lot. ^_^