# confidence interval

#### rgentil32

##### New Member
With the following data (male):
Mean 47.281
Stand. E 1.615
Stand. D 11.53
Count (N?) 51

I estimated the 95% confidence interval for the mean salary for male faculty members to be $44,037 to$50,526.

Given this data (female):
Mean 43.195
Stand. E 1.16
Stand. D 10.636
Count (N?) 83

How do I find critical t-values for 90% and 95% CI?
How do I calculate the standard error for the mean salary in pop. of female?
How do i find upper and lower bounds of the 90% and 95% CI for the mean salary in pop. of female?

(I realize alot of questions, I need a starting point...the help with the z-scores was fantastic)
Rick

#### JohnM

##### TS Contributor
How do I find critical t-values for 90% and 95% CI?
Look up the two-tailed values for t in the t-table in your text, using the significance level and degrees of freedom

How do I calculate the standard error for the mean salary in pop. of female?
This is given to you: 1.16
It's computed by: std dev/sqrt(n)

How do i find upper and lower bounds of the 90% and 95% CI for the mean salary in pop. of female?
Look in our Examples section - there's a post called Computing Confidence Intervals - we talk about how to use the t distribution

confidence interval = mean +/- (statistic * std dev/sqrt(n))
where statistic is t for small samples and Z for large samples