A Brief Note on Overlapping Confidence Intervals
Clinical researchers frequently assess the statistical significance of the difference between two means by examining whether the two 95% confidence intervals overlap. The purpose of this brief communication is to illustrate that the 95% confidence intervals for two means can overlap and yet the two means can be statistically significantly different from one another at the α = 0.05 level
Peter C. Austin. "A Brief Note on Overlapping Confidence Intervals" Journal of Vascular Surgery 36 (2002): 194-195.