Question 7.36

7.36 Design of controls.

The design of controls and instruments has a large effect on 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 by screw action. 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 turns counterclockwise). The following table gives the times required (in seconds) to move the indicator a fixed distance:17

cntrols

Subject Right
thread		 Left
thread		 Subject Right
thread		 Left
thread
1 113 137 14 107 87
2 105 105 15 118 166
3 130 133 16 103 146
4 101 108 17 111 123
5 138 115 18 104 135
6 118 170 19 111 112
7 87 103 20 89 93
8 116 145 21 78 76
9 75 78 22 100 116
10 96 107 23 89 78
11 122 84 24 85 101
12 103 148 25 88 123
13 116 147
  1. Each of the 25 students used both instruments. Discuss briefly how the experiment should be arranged and how randomization should be used.
  2. The project hoped to show that right-handed people find right-hand threads easier to use. State the appropriate and about the mean time required to complete the task.
  3. Carry out a test of your hypotheses. Give the -value and report your conclusions.