Simulation Study on Sample Size of Exposure Assessment

In the process of exposure assessment,how to determine the sample size to obtain the most economic and effective percentile estimation has seldom been studied.With the benefit of computer simulation,this paper sets out to explore the relationship with 4 positively skewed distributions.And the lognormal distribution has been further selected to study the impact of distribution pattern and variation on percentile estimates.The simulation results showed as follows:(1)Accurately estimating a higher percentile of the positively skewed distribution would require a larger sample size.And a larger sample size always results in a more accurate and more stable estimated percentile.With a sample size of 500,we accurately estimated all the target percentiles of the 4 positively skewed distributions except the result of P99.9.(2)Estimating the same percentile using lognormal distribution required far larger sample size than it needed when using a normal distribution.Moreover,the sample size needed for a lognormal distribution estimation was positively correlated to the magnitude of the variation of the skewed distribution. This research would be very helpful to the exposure assessment in determining the sample size during the survey period.