Who can tell me something about degree of freedom in statistic?

[The Bug]

being stuck by standard deviation, I just can't understand the difference between n and n-1.
who can give me some concrete examples?
thank you!

 

[chiro]

being stuck by standard deviation, I just can't understand the difference between n and n-1.
who can give me some concrete examples?
thank you!

Are you referring to the estimated standard deviation vs the actual standard deviation?

If so the reason is because the (n-1) term has to do with the fact that dividing by (n-1) instead of n will result in an unbiased point estimator of the variance and hence standard deviation.

Basically for unbiased estimators you have to show that E[σ_est²] = E[σ²] and what this ends up doing is forcing you to use the (n-1) in terms of n.