• Jan 21st 2010, 09:56 AM
axa121
Hi I', doing a question on confidence intervals, could someone please check if I have the right answer please.

Here is the question:

Males:
n = 25
x bar = 47.8
$\displaystyle s^2$ = 25.6
d bar = 3.32
$\displaystyle s^2 d$ = 7.13

Females:
n = 20
x bar = 30
$\displaystyle s^2$ = 24.7
d bar = 1.52
$\displaystyle s^2 d$ = 5.38

The question asks to estimate whether or not the average difference in grip difference(d bar) is greater among males than among females and asks to comment on the interval.

Here is what is did, but I'm not sure if I have the right answer:

d bar males - d bar females $\displaystyle \pm$ t(n1,n2 -2; 0.975) x $\displaystyle \sqrt {s^2p (1/n1 + 1/ n2)}$

= 3.32 - 1.15 $\displaystyle \pm$ 2.0175 * 0.7567
= (0.644, 3.696)

Thanks.
• Jan 24th 2010, 09:54 PM
matheagle
I'm not sure what this d bar is.
The degrees of freedom is $\displaystyle n_1+n_2-2$
But this if we assume that the population variances are equal.
• Jan 25th 2010, 05:49 AM
axa121
Hi, d bar is the difference in grip strength between the left and right hand. In the question is does assume that the variances are equal.

I'm not sure if I have calculated it right though.