Bignert Anders, Riget Frank, Braune Birgit, Outridge Peter, Wilson Simon
Contaminant Research Group, Swedish Museum of Natural History, PO Box 50 007, S-104 05 Stockholm, Sweden.
J Environ Monit. 2004 Apr;6(4):351-5. doi: 10.1039/b312118f. Epub 2004 Mar 10.
The goal of this paper is to describe and discuss statistical power with respect to mercury in Arctic biota, using data gathered during the past two or three decades, mostly under the auspices of AMAP Phases I and II. It will describe the current levels of power of existing data sets to detect temporal trends of Hg concentrations. If the desired power is fixed to an appropriate magnitude, the minimum size of a detectable trend within a specified time period or the number of years that is required to detect a certain trend could be estimated provided that the random between-year variation for the current time-series is known. These various measures of performance of the AMAP mercury time-series, derived from the power analysis, are discussed in some detail. The number of years required to detect a certain trend at a particular power at a specific Type I error rate (alpha) is compared with the actual number of years available when the AMAP Phase II assessment was carried out. In general the investigated time-series were too short to possess an acceptable statistical power. The effect of varying the Type-I error rate, the slope of a trend and the desired power is investigated to rank the importance of the various components regulating the statistical power. The consequence of sampling less frequently than once a year is considerable loss of power.
本文的目的是利用过去二三十年收集的数据（主要是在北极监测与评估计划第一阶段和第二阶段的支持下收集的），描述和讨论北极生物群中汞含量的统计功效。它将描述现有数据集检测汞浓度时间趋势的当前功效水平。如果将所需功效固定在适当的幅度，那么在已知当前时间序列的年际随机变化的情况下，就可以估计在特定时间段内可检测趋势的最小规模或检测特定趋势所需的年数。本文将详细讨论从功效分析得出的北极监测与评估计划汞时间序列的这些不同性能指标。将在特定的I型错误率（α）下以特定功效检测特定趋势所需的年数与进行北极监测与评估计划第二阶段评估时可用的实际年数进行比较。总体而言，所研究的时间序列太短，无法拥有可接受的统计功效。研究了改变I型错误率、趋势斜率和所需功效的影响，以对调节统计功效的各个组成部分的重要性进行排序。每年采样频率低于一次的后果是功效大幅损失。
