Kaune W T, Feychting M, Ahlbom A, Ulrich R M, Savitz D A
EM Factors, Richland, Washington 99352, USA.
Bioelectromagnetics. 1998;19(6):354-65.
A recent study conducted in Sweden reported that 1) leukemia risk in children who lived near 220 or 400 kV electric-power transmission lines was associated with calculated historical magnetic field levels; 2) children living within a distance of 50 m of transmission lines had an elevated risk of leukemia; and 3) there was no association between leukemia and residential magnetic fields measured many years after diagnosis. Subsequently, these investigators found through logistic regression analysis that disease was more strongly associated with calculated historical fields than with distance. Since the calculated historical fields in that study depended predominantly on distance and transmission-line load current, the logistic regression results suggest that historical load current plays an important role in the epidemiological results. Thus, we studied hourly 1974 load-current data for six transmission lines, and we examined 1958-1985 annual load-current data for 112 transmission lines. Most lines exhibited marked diurnal load-current rhythms during 1974, and all six showed systematic weekday-weekend differences. During 1958-1985, average loadings of Swedish 220 and 400 kV lines increased by about 1.3% year. Predictive-value and kappa-statistic analyses indicated that Swedish transmission-line load currents were not stable over long periods, so that contemporaneous load current (or a contemporary magnetic field measurement) was not a good surrogate for historical load current (or historical magnetic fields). The results provide a potential explanation of the failure of the Swedish Study to find an association between leukemia and contemporaneous magnetic field levels measured many years after the etiologic period, and suggest that the inclusion of load-current data could significantly improve the quality of historical field calculations.
1）居住在220千伏或400千伏输电线路附近的儿童患白血病的风险与计算出的历史磁场水平相关；2）居住在距离输电线路50米以内的儿童患白血病的风险升高；3）白血病与诊断多年后测量的居住磁场之间没有关联。随后，这些研究人员通过逻辑回归分析发现，疾病与计算出的历史磁场的关联比与距离的关联更强。由于该研究中计算出的历史磁场主要取决于距离和输电线路负载电流，逻辑回归结果表明历史负载电流在流行病学结果中起着重要作用。因此，我们研究了六条输电线路1974年的每小时负载电流数据，并检查了112条输电线路1958 - 1985年的年度负载电流数据。1974年，大多数线路呈现出明显的日负载电流节律，所有六条线路都表现出工作日 - 周末的系统性差异。在1958 - 1985年期间，瑞典220千伏和400千伏线路的平均负载每年增加约1.3%。预测值和kappa统计分析表明，瑞典输电线路的负载电流在很长一段时间内不稳定，因此同期负载电流（或当代磁场测量值）不是历史负载电流（或历史磁场）的良好替代指标。这些结果为瑞典研究未能发现白血病与病因期多年后测量的同期磁场水平之间的关联提供了一个潜在的解释，并表明纳入负载电流数据可以显著提高历史磁场计算的质量。
