The work attendance data were pooled to enable the percentage of maintenance
personnel present at work at each hour of the day to be estimated
(Figure 1). It can be seen, for example, that between 35 and 40% of
respondents indicated that they were at work between 01:00 and 05:00 h
during their most recently worked shift, and over 50% of workers
reported being at work between 08:00 and 16:00 h. A correction factor
was calculated to express the difference between the estimated percentage
of personnel present at work each hour and a nominal value of 50% work
attendance. Error frequencies were then multiplied by the correction
factor to arrive at the number of errors expected if an equal number of
workers had been present at work each hour of the day.