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 Page 2right hands) that moved an indicator by screw action. There were two identical instruments, one with right-hand thread (the knob turns clockwise) and the other with a left-hand thread (the knob turns counterclockwise). The table below gives the times in seconds each subject took to move the indicator a fixed distance.
(a) Each of the 25 students used both instruments. Discuss briefly how you would use randomization in arranging the experiment.
(b) The project hoped to show that right-handed people find right-hand threads easier to use. Do an analysis that leads to a conclusion about this issue.
Performance times (seconds) using right-hand and left-hand threads
|
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
|
1 1 1
|
123
|
|
5
|
136
|
115
|
18
|
104
|
135
|
|
6
|
118
|
170
|
19
|
1 1 1
|
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
|
11
|
|
12
|
103
|
148
|
25
|
88
|
123
|
|
13
|
116
|
147
|
|
|
|