Highway safety engineers test new road signs, hoping that increased reflectivity

Question

Highway safety engineers test new road signs, hoping that increased reflectivity will make them more visible to drivers. Volunteers drive through a test course with several of the new- and old-style signs and rate which kind shows up the best. Is this a one-tailed or a two-tailed test? It is one-tailed (one-sided) test. It is two-tailed (two-sided) test. A 95% confidence interval for the difference between two means is reported as (-2.8, -1.3). What can you conclude about the results of significance test for the null hypothesis that the population means are equal versus the two-sided alternative?

Explanation / Answer

Ans 1: It is a one tail test as they want to see if increased reflectivity made it more visible or not.

Ans 2: The 95% confidence interval is providing a range that you are 95% confident the true difference in means falls in. Thus, the CI can include negative numbers, because the difference in means may be negative.

If a difference between two means is 0, then the twomeans are equal!] Confidence intervals contain population values found to be consistent with the data. If a confidence interval for a mean difference includes 0, the data are consistent with a population mean difference of 0. So, if it doesnt include zer (our case) null is rejected and alternative is accepted.

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