The article “Time Series Analysis for Construction Productivity Experiments” (T. Abdelhamid 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. A lift of moderate difficulty was performed several times, both with the new video system and with the old tagman system.

The time (in seconds) required to perform each lift was recorded. The following table presents the means, standard deviations, and sample sizes.

Standard Sample Mean Deviation Size Tagman 69.33 6.26 12 Video 58.50 5.59 24 Can you conclude that the mean time to perform a lift is less when using the video system than when using the tagman system? Explain.