Tool design $($weight$,$ shape, fit to the user and the task$),$ workstation design $($size$,$ shape and layout$),$ and the way tasks are scheduled are all key factors in making hand tool use safe and risk$-$free. An effective prevention strategy must address all aspects at the same time. Ergonomic design of tools is important for reducing the risk of work$-$related musculoskeletal disorders. Also of great interest is the extent to which the tool design leads to efficient use of human energy thereby increasing process efficiency.

Problem Details

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 right$-$handed thread $($the knob turns clockwise$)$ and the other with a left$-$handed thread $($the knob turns counterclockwise$).$ The times $($in seconds$)$ required to move the indicator a fixed distance were recorded and can be found in the $$Part II Turn Times$$ worksheet in the Excel file titled $$Case #$1$ Data.$$

Requirements $($see Rubric on page $6$ of these instructions for additional details$)$

$1.$ Carry out a test using a P$-$value to determine if right$-$handed people find using right$-$hand threads more efficient. Use a significance level of $0\mathrm{.}05.$

$2.$ Include a confidence interval that estimates the mean time advantage of right$-$hand over left$-$hand threads to go with the test. Be careful about the confidence level!

$3.$ Briefly discuss the practical importance of the time difference between the right$-$hand and left$-$hand threaded tools. In particular, consider that an assembly$-$line worker may perform the task many times in a shift. It might be informative to consider the mean time for right$-$hand threads as a percent of the mean time for left$-$hand threads.

$4.$ Complete the analysis using the PLAN $$ DO $$ REPORT format to detail the problem, your work, and your conclusions$\backslash$table$[[$Subject$,$Right,Left$],[1,113,137],[2,105,105],[3,130,133],[4,101,108],[5,138,115],[6,118,170],[7,87,103],[8,116,145],[9,75,78],[10,96,107],[11,122,84],[12,103,148],[13,116,147],[14,107,105],[15,118,166],[16,103,146],[17,111,123],[18,104,135],[19,111,112],[20,89,93],[21,78,76],[22,100,116],[23,89,90],[24,85,101],[25,88,123]]$