Sign up ×  This is a paired comparison questionenter image
description here:  The answer is: enter image description here
However, this is my thought of using a t test on difference of
population means  enter image description here
$$t=\frac{583.125 - 415 -
0}{\sqrt{\frac{262.5900866^2}{8}+\frac{261.5721698^2}{8}}}$$
$t= 1.2829$  enter image description here   critital value
$t_{0.05}(df=14)$= 1.76131  $1.2829 < 1.76131$  therefore no
difference between the mean daily sales from the two stores. Why
am I getting a different conclusion? Is it reasonable to think
about it this way?  share|cite|improve this question I suppose
$s_1^2$ is the sample variance of $\bar{x}_1$ and $s_2^2$ is the
sample variance of $\bar{x}_2$. In that case, the sample
variance of $\bar{x}_{1}-\bar{x}_{2}$ is not equal to the sum of
variance unless covariance is equal to zero. Hence, the
denominator of your statistics does not seem to be correct.
Moreover, the degrees of freedom are 7 because you only lose 1
observation when computin