A note on confidence intervals and statistical significance
If two 95% confidence intervals overlap this does not imply that the two statistics on whicb they are based (e.g. means, odds ratios) differ at the 5 percent level. In other words it is possible for the difference between two statistics to be statistically non-zero and for their respective confidence intervals still to overlap. This is usually the case when the difference between the means has moderate significance.
It is true, however, that if a pair of confidence intervals do not overlap the difference between the two statistics is statistically non-zero.
The rationale behind the above discrepancy is explained in this [attachment:cis.pdf article] taken from the Cornell University website.