Right versus left The design of controls and instruments affects how easily people can

QUESTION:

Right versus left The design of controls and instruments affects how easily people can use them. A student project investigated this effect by asking 25 right-handed students to turn a knob (with their right hands) that moved an indicator. There were two identical instruments, one with a right-hand thread (the knob turns clockwise) and the other with a left-hand thread (the knob must be turned counterclockwise). Each of the 25 students used both instruments in a random order. The following table gives the times in seconds each subject took to move the indicator a fixed distance.23 Note that smaller times are better. Subject Right thread Left thread 1 113 137 2 105 105 3 130 133 4 101 108 5 138 115 6 118 170 7 87 103 8 116 145 9 75 78 10 96 107 11 122 84 12 103 148 13 116 147 14 107 87 15 118 166 16 103 146 17 111 123 18 104 135 19 111 112 20 89 93 21 78 76 22 100 116 23 89 78 24 85 101 25 88 123 (a) Explain why it was important to randomly assign the order in which each subject used the two knobs. (b) The project designers hoped to show that righthanded people find right-hand threads easier to use, on average. Carry out a test at the 5% significance level to investigate this claim.