Resumen
Human beings have naturally different variations in performance which may lead towards significant differences between the results forecasted by simulation models and those actually obtained. Current research studies the effects of human factors such as circadian rhythms and variations in workday shifts on operators´ performance. It also proposes a method for collecting time data in assembly lines, which takes into consideration different time periods for each work shift to apprehend the variability of human performance at different points throughout the day. The new method was applied in an industrial process with a high rate of manual labor and its production results on the shifts were compared. Results reveal that human factors have a significant impact on the simulation model, providing results closer to reality, which, in turn, lead to more accurate production forecasts.