9-2 Two Means: Independent Samples 465 b. Construct the confidence interval suitable for testing the claim in part (a). No Candy: n = 20, x = 18.95, s = 1.50 Two candies: n = 20, x = 21.62, s = 2.51 6. Readability of Font On a Computer Screen The statistics shown below were obtained from a standard test of readability of fonts on a computer screen (based on data from “Reading on the Computer Screen: Does Font Type Have Effects on Web Text Readability?” by Ali et al., International Education Studies, Vol. 6, No. 3). Reading speed and accuracy were combined into a readability performance score (x), where a higher score represents better font readability. a. Use a 0.05 significance level to test the claim that there is no significant difference in readability between Roman and Arial fonts. b. Construct the confidence interval suitable for testing the claim in part (a). Roman: n = 24, x = 66.25, s = 12.96 Arial: n = 24, x = 65.62, s = 9.93 7. Hand Cleansing An experiment was conducted to determine whether there is a difference between washing hands with antiseptic soap and rubbing hands with an alcohol based solution. Hand bacteria counts were measured in colony forming units (cfu) with the results summarized below (based on data from “Efficacy of Handrubbing With Alcohol Based Solution versus Standard Handwashing with Antiseptic Soap,” by Girou et al., British Medical Journal). a. Use a 0.01 significance level to test the claim that rubbing with alcohol results in a lower bacteria count. b. Construct the confidence interval suitable for testing the claim in part (a). c. Does the conclusion change if the significance level is changed to 0.05? Washing With Soap: n = 55, x = 69, s = 106 Rubbing With Alcohol: n = 59, x = 35, s = 59 8. Birth Weights Listed below are birth weight statistics from Data Set 6 “Births” in Appendix B. a. Use a 0.01 significance level to test the claim that at birth, girls have a lower mean weight than boys. b. Construct the confidence interval suitable for testing the claim in part (a). Girls: n = 205, x = 3037.1 g, s = 706.3 g Boys: n = 195, x = 3272.8 g, s = 660.2 g 9. Color and Cognition Researchers from the University of British Columbia conducted a study to investigate the effects of color on cognitive tasks. Words were displayed on a computer screen with background colors of red and blue. Results from scores on a test of word recall are given below. Higher scores correspond to greater word recall. a. Use a 0.05 significance level to test the claim that the samples are from populations with the same mean. b. Construct a confidence interval appropriate for the hypothesis test in part (a). What is it about the confidence interval that causes us to reach the same conclusion from part (a)? c. Does the background color appear to have an effect on word recall scores? If so, which color appears to be associated with higher word memory recall scores? Red Background n = 35, x = 15.89, s = 5.90 Blue Background n = 36, x = 12.31, s = 5.48
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