The design of instrument controls affects how easily people can use them. An investigator used 25 students who were right-handed to determine whether right-handed subjects preferred right-handed threaded knobs. He had two machines that differed only in that one had a knob that turned in a clockwise fashion (right-handed threads), and the other had a knob that turned in a counterclockwise fashion, (left-handed threads). Turning the knobs moved an indicator bar on a scale. The investigator timed how many seconds it took each subject to move the bar a set distance, using each of the two machines, but only their right hand. So, each of the 25 subjects used only their right hand on the two machines, turning one knob clockwise and the other counterclockwise.
a) Explain briefly how you would use randomization in arranging this experiment
b) Do an analysis to determine if the data shows that right-handed people are FASTER, or need LESS time, to operate knobs with right-handed threads that turn in a clockwise fashion compared to knobs that turn in a counterclockwise fashion.
c) Construct a 95% confidence interval for the mean time advantage of clockwise over counterclockwise threads for this group of subjects.
d) Are clockwise threaded knobs more efficient for right-handed people? What is the ratio, expressed as a percent, of the mean time for using clockwise threads compared to the mean time for using counterclockwise threads?