Statistical and Practical Significance (2 of 4)
The 95% confidence interval on the difference between means is:
-7.0 ≤ μcolor - μblack & white ≤ -0.1
which means that the experimenter can be confident that the color display is between 7.0 seconds and 0.1 seconds faster. Clearly, the difference is not big enough to justify the more expensive color displays. Even the upper limit of the 95% confidence interval (seven seconds) is below the minimum needed to justify the cost (10 seconds). Therefore, the experimenter could feel confident in his or her recommendation that the black and white displays should be used. The fact that the color displays were significantly faster does not mean that they were much faster. It just means that the experimenter can reject the null hypothesis that there is no difference between the displays.