Hoozemans M J, Burdorf A, van der Beek A J, Frings-Dresen M H, Mathiassen S E
Coronel Institute for Occupational and Environmental Health, AmCOGG Amsterdam Center for Research into Health and Health Care, Academic Medical Center, University of Amsterdam, The Netherlands.
Scand J Work Environ Health. 2001 Apr;27(2):125-32. doi: 10.5271/sjweh.599.
The precision of mean exposure to pushing was examined in 2 occupational groups using various combinations of the number of workers and measurements per worker.
The frequency and duration of pushing of the 2 occupational groups was assessed using onsite observation. All data were divided into successive periods of 30 minutes of observation. The precision of the group mean exposure to pushing was expressed by 90% confidence intervals obtained by bootstrapping. The effect on the confidence interval of varying numbers of workers and numbers of periods per worker was examined.
For both occupational groups there was little precision to be gained when >10 workers were observed. Within the maximum number of workers used in the bootstrap simulations, it appeared that, beyond 10 workers, the confidence intervals decreased by <5% for every worker that was added, when each worker was observed at least 8 periods of 30 minutes. If workers were observed exactly 4 periods of 30 minutes per worker, an additional 4 workers were required to compensate for the loss of precision. An unbalanced strategy with approximately 8 periods of 30 minutes per worker hardly decreased the precision of the group mean, however.
The precision of the group-based mean exposure to pushing is influenced by the number of workers observed and by the number of repeated measurements per worker. In the planning of measurement strategies, it is advisable to account for possible sources of variance in advance and to assess the exposure variability.
在两个职业群体中，使用不同的工人数量组合以及每个工人的测量次数，检验推挤平均暴露量的精确性。
通过现场观察评估两个职业群体推挤的频率和持续时间。所有数据被分为连续的30分钟观察时段。推挤群体平均暴露量的精确性通过自抽样法得到的90%置信区间来表示。研究了工人数量和每个工人观察时段数量变化对置信区间的影响。
对于两个职业群体，当观察超过10名工人时，精确性提升不大。在自抽样模拟使用的最大工人数量范围内，当每个工人至少被观察8个30分钟时段时，似乎超过10名工人后，每增加一名工人，置信区间缩小不到5%。如果每个工人恰好被观察4个30分钟时段，则需要额外增加4名工人来弥补精确性的损失。然而，每个工人采用大约8个30分钟时段的不平衡策略几乎不会降低群体均值的精确性。
基于群体的推挤平均暴露量的精确性受观察的工人数量以及每个工人重复测量次数的影响。在测量策略规划中，建议提前考虑可能的方差来源并评估暴露变异性。
