The article “Time Series Analysis for Construction Productivity Experiments” (T. Abdel hamid and J. Everett, Journal of Construction Engineering and Management, 1999:87–95) presents a study comparing the effectiveness of a video system that allows a crane operator to see the lifting point while operating the crane with the old system in which the operator relies on hand signals from a tagman. Three different lifts, A, B, and C, were studied. Lift A was of little difficulty, lift B was of moderate difficulty, and lift C was of high difficulty. Each lift was performed several times, both with the newvideo system and with the old tagman system. The time (in seconds) required to perform each lift was recorded. The following tables present the means, standard deviations, and sample sizes.
| High Difficulty | |||
| Standard | Sample | ||
| Mean | Deviation | Size | |
| Tagman | 109.71 | 17.02 | 17 |
| Video | 84.52 | 13.51 | 29 |
a. Can you conclude that the mean time to perform a lift of low difficulty is less when using the video system than when using the tagman system? Explain.
b. Can you conclude that the mean time to perform a lift of moderate difficulty is less when using the video system than when using the tagman system? Explain.
c. Can you conclude that the mean time to perform a lift of high difficulty is less when using the video system than when using the tagman system? Explain.
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