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Work pattern causes bias in self-reported activity duration: randomized study of mechanisms and implications for exposure assessment and epidemiology
  1. Lope H Barrero (lbarrero{at}
  1. Harvard School of Public Health, United States
    1. Jeffrey N Katz (jnkatz{at}
    1. Brigham and Women's Hospital, United States
      1. Melissa J Perry (mperry{at}
      1. Harvard School of Public Health, United States
        1. Ramaswamy Krishnan (rkrishna{at}
        1. Harvard School of Public Health, United States
          1. James H Ware (ware{at}
          1. Harvard School of Public Health, United States
            1. Jack T Dennerlein (jax{at}
            1. Harvard School of Public Health, United States


              Background: Self-reported activity duration is commonly used to estimate cumulative exposures in epidemiological research. The validity of self-reported duration of exposure has been estimated previously in observational studies but not in experimental studies; however, observational designs limit the accuracy of validation and also limit investigation of the sources of error.

              Objective: This laboratory experiment investigates the effects of work pattern, self-reported task dullness (a measure of cognitive task demand), and task heart rate ratio and perceived physical exertion (measures of physical task demands) on the error in task duration estimation.

              Methods: Twenty-four participants (23-to-54-years, 12 males, 12 females), recruited from the working population, were randomly assigned to execute three tasks in either a continuous (three periods of 40 continuous minutes, one for each task) or a discontinuous work pattern (40-minute tasks each divided into four periods of 4, 8, 12 and 16 minutes). Heart rate was measured during the tasks. After completing the two-hour work session, subjects reported the perceived duration, dullness and physical exertion for each of the three tasks. Multivariate models were fitted to analyze errors and their absolute value to assess the accuracy in task duration estimation and the mediating role of task demands on the observed results.

              Results: Participants overestimated the time spent shelving boxes (up to 38%) and filing journals (up to 9%), and underestimated the time typing articles (up to -22%). Over and underestimates were greater in the discontinuous work pattern group. Absolute errors also were larger for the discontinuous work pattern. Only the self-reported task dullness mediated the differences in task duration estimation accuracy between work patterns.

              Conclusions: Task-related factors can affect self-reported activity duration. Exposure assessment strategies that require persons to allocate work time to different tasks could result in biased measures of association depending on the demands of the tasks during which the exposure of interest occurs.

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