臺灣博碩士論文加值系統

背景目的：世界衛生組織所屬國際癌症總署在其2002年的報告指出：15歲以下學童的白血病發生可能與環境中極低頻磁場（ELF-MF）之暴露（＞4 milli-Gauss，mG）有關，因此推斷15歲以下學童可能是最容易受到極低頻磁場危害的主要族群。礙於極低頻磁場須仰賴科學儀器定量且在有限的研究經費及受測者配合度等條件之限制，使得多數流行病學研究僅能進行瞬間或短時間的磁場測量，因此短時間之磁場測量數值能否用以代表較長時間的極低頻磁場暴露強度便成為研究關心之議題。此外，利用何種統計量做為長時間磁場測量之摘要暴露參數亦有許多討論。本研究嘗試利用227位學齡兒童（7～15歲）個人連續24-h極低頻磁場測量值（1次∕6秒）及其個人活動日誌，探討學童於一日內各時段別所經歷之磁場暴露強度以及與個人連續24-h磁場測值間之相關情形，同時也探討極低頻磁場各暴露參數間之相關性。
材料方法：本研究資料來源為李氏先前所執行之環保署研究計畫，從參與研究的北台灣32所學校中選取有受試意願之227名國民中小學學童樣本，進行個人連續24-h極低頻磁場測量。依研究對象所紀錄之活動日誌將個人24-h磁場測量值區分成校園室內、校園室外、課後輔導環境、家中非睡眠以及睡眠時段等時間區塊，計算每位學童於各時段及連續24-h磁場測值之算術平均數、幾何平均數、算術標準差、幾何標準差、變異係數、磁場平均改變強度、磁場強度＞3 mG與 ＞4 mG之時間百分比等暴露參數，並利用Spearman correlation coefficient、Kappa統計量、敏感度以及特異度比較各時段與個人連續24-h磁場暴露間之參數別相關性，以及用Spearman correlation coefficient評估個人連續24-h磁場測量值各類暴露參數間之相關性。
結果：參加本研究的227位學童之個人連續24-h磁場測值算術平均數之平均值為1.76 ± 1.77 mG，其中個人連續24-h磁場算術平均值強度＞3 mG以及＞4 mG以上之人數分別為14.5 ％、3.52 ％；時段別磁場暴露強度則以課後輔導時段強度居冠（2.52 ± 3.79 mG），校園的室外環境最低（1.24 ± 1.16 mG）；而課後輔導時段也有最高之磁場閾值（＞3∕4 mG時間％）及類別型態（＞3∕4 mG人數％）參數暴露強度。此外，個人連續24-h磁場測值之集中趨勢與閾值型態暴露參數間之相關程度較高（r＝0.69～0.86），而與離散趨勢參數之相關性則較低（r＝-0.26～0.70）；各時段別與連續24-h極低頻磁場測量值間之暴露參數別相關性分析結果顯示，集中趨勢與閾值型態參數間具有較好之相關性。至於學童個人連續24-h磁場測值的算術平均值強度預測方面，則是以家中時段的磁場測值預測能力較佳，而校園時段磁場測值之預測能力則相對較差。
結論：本研究結果顯示，此都會樣本學齡兒童於課後輔導時段之磁場暴露強度為全天各時段中最高者，顯示關注學童於課後輔導環境極低頻磁場暴露之重要性。此外，如在研究資源受限的情況下，可僅取學童於家中非睡眠時段的環境極低頻磁場測量值來預測學童個人連續24-h之磁場暴露程度；本研究也建議分析長時間磁場暴露值時不僅要計算測值之算術平均數，更要搭配任一離散趨勢暴露參數，如此較能完整的作為代表學童個人連續24-h暴露程度之指標。

Background and Objectives: The International Agency for Research on Cancer affiliated with the World Health Organization reported in 2002 that environmental exposure ( >4 milli-Gauss, mG) to extremely-low-frequency magnetic field (ELF-MF) is a possible cause of leukemia in children aged 15 years or less, suggesting that children are potentially vulnerable to the leukemogenic risk posed by ELF-MF exposure. Because ELF-MF can only be quantified by instrumental dosimetry, which is usually costly and less comfortable perceived by the study subjects being measured, many epidemiological studies alternatively performed “spot” or “short-term” measurements of ELF-MF. However, it has not been very clear whether the data taken from a short-term period can be well representative of long-term exposure. Additionally, there has been a lot of discussion regarding what summary measures are the best representative of long-term continuously measured data. This study used the data of 24-h continuously measured ELF-MF (sampling interval：1∕6 sec.) along with the logged diaries among 227 school children (7～15 years of age) to quantify children’s ELF-MF exposure levels at different time periods during a day and their respective associations with 24-hr exposure level. This study also explored the inter-correlations among various 24-h exposure parameters.
Materials and Methods: Data used in this study were obtained from a previous Taiwan EPA sponsored research project conducted by Li. This project collected 24-h continuously measured personal ELF-MF among 227 children from 32 elementary and junior high schools in northern Taiwan. Based the logged diary, the 24-h ELF-MF data were was divided into several time periods with specific exposure levels, including periods for indoor and outdoor environments at campus, day care center after-school, and non-sleep and sleep time at home. Various exposure parameters, including arithmetic and geometric means (AM∕GM) (standard deviations, SD), coefficient of variation (CV), rate of change metric, and proportions of time ＞3 mG and 4 mG, were calculated for each time period during a day. Using Spearman correlation coefficient, sensitivity, and specificity, this study examined the exposure parameters-specific associations between 24-h exposure and the exposure at each time period. The inter-correlations among exposure parameters in 24-h were assessed by Spearman correlation coefficient and Kappa statistic.
Results: The average 24-h AM was 1.76 ± 1.77 mG for the study children. The estimated proportion of children with the 24-h AM exposure levels of > 3 mG or > 4 mG was 14.5% or 3.52%, respectively. The highest (2.52 ± 3.79 mG) and the lowest (1.24 ± 1.16 mG) time period specific AM exposure was noted at after-school day care centers and outdoor areas at campus, respectively. The after-school day care centers also had higher threshold（% of time ＞3∕4 mG）and categorical exposure parameters（% of individuals ＞3∕4 mG）. Additionally, the 24-h central tendency exposure parameters had high associations with the threshold exposure parameters（r＝0.69～0.86）, but had lower associations with dispersion exposure parameters（r＝-0.26～0.70）. The analyses of parameters-specific exposure associations between exposures at various time periods and that of 24-h showed that the association between short term measures and 24-h measures were higher for central tendency and threshold parameters. The data also showed that the AM of exposure to ELF-MF measured at home was able to well predict the 24-h AM, whereas that measured at campus showed a poor predictive capability.
Conclusions: This study indicated that children’s exposure to ELF-MF at after-school day care centers was high in this urban sample, suggesting a need for concern regarding children’s exposure in that environment. Additionally, home exposure to ELF-MF during non-sleep hours can be alternatively used as children’s 24-h exposure level, if long term measurements were not possible due to limited resources. This study also suggests that both central tendency and dispersion exposure parameters should be calculated simultaneously as exposure indices in order to better represent children’s 24-h exposure.

總目錄
摘 要 I
英文摘要 IV
總目錄 VII
圖目錄 XI
第壹章 緒論 1
第一節 研究背景 1
第二節 研究目的 5
第貳章 文獻探討 7
第ㄧ節、極低頻電磁場之簡介 7
一、極低頻電磁場之物理特性 7
二、環境中極低頻磁場的來源與暴露強度 8
三、極低頻磁場與人體健康效應之流行病學研究 10
第二節、環境中極低頻磁場的暴露評估方法 11
一、磁場測量方法 11
二、磁場暴露計量與參數 16
第三節、極低頻磁場暴露參數相關性之研究 19
第四節、不同時段（或地點）所測磁場強度之相關性 21
一、住家環境磁場測量 21
二、個人磁場測量 25
三、個人與住宅環境磁場測量值間之一致性 28
第參章 材料與方法 32
第一節 研究資料 32
一、選樣方法 32
二、測量程序 33
第二節 資料分析 34
一、資料處理 34
二、暴露參數間之相關性分析 35
三、短時間與24-h暴露參數間之相關性分析 37
第肆章 研究結果 38
第一節 研究樣本描述 38
ㄧ、研究對象基本特性 38
二、研究對象連續磁場測值之各式描述性統計 38
第二節 暴露參數之相關性分析 41
一、研究樣本24-h磁場測量值暴露參數間之相關性 41
二、研究樣本各時段與24-h磁場測值暴露參數間之相關性 43
第伍章 討論 49
第一節 研究結果摘要整理 49
第二節 學童極低頻磁場暴露參數之探討 50
第三節 學童磁場暴露狀況之比較以及時段別與24-h磁場強度相關性比較之討論 51
第四節 本研究之優缺點 56
第五節 結論與建議 58
參考文獻 59

表目錄
表 1、使用極低頻測量儀器進行直接測量的研究 66
表 2、研究樣本年級別以及校園地理區域之分布 67
表 3、研究樣本24–h及各時段內磁場測量值暴露參數之描述性統計 68
表 4、研究樣本24-h及各時段內磁場測量值暴露參數之分布情形 69
表 5、研究樣本24-h測量值之各連續性暴露參數間之相關係數. 71
表 6、研究樣本24-h磁場測值各連續性與類別性暴露參數間之相關性 72
表 7、研究樣本24-h與各時段內相同暴露參數間之相關性 73
表 8、24-h與各時段磁場類別性暴露參數之一致性（平均值＞3 mG） 74
表 9、24-h與各時段磁場類別性暴露參數之一致性（平均值＞4 mG） 75
表 10、研究樣本24-h與各時段磁場測值（經抽樣後）內相同暴露參數間之相關性 76
表 11、24-h與各時段（經抽樣後）磁場類別性暴露參數之一致性（平均值＞3 mG）77
表 12、24-h與各時段（經抽樣後）磁場類別性暴露參數之一致性（平均值＞4 mG）78
表 13、學童個人長時間磁場暴露的相關研究結果 79

圖目錄
圖 1、學童進行個人測量所使用的極低頻磁場測量儀器EMDEX II及其規格 80
圖 2、學童進行個人測量所使用的極低頻磁場測量儀器EMDEX LITE及其規格 81
圖 3、學童個人24-h極低頻磁場連續測值資料範例 82
圖 4、學童個人24-h活動日誌紀錄之格式與內容範例 83
圖 5、學童個人24-h極低頻磁場測值之時段分割範例 84
圖 6、所有學童個人磁場平均暴露強度人數累積百分比 85
圖7、研究樣本（n＝227）各類24-h極低頻磁場暴露參數之箱形圖 86
圖8、研究樣本（n＝227）變異係數之箱形圖 87
圖9、研究樣本（n＝227）24-h極低頻磁場測量值＞3 mG或＞4 mG之時間百分比分布箱型圖88
圖10、校園暴露組學童個人磁場平均暴露強度人數累積百分比 89
圖11、校園對照組學童個人磁場平均暴露強度人數累積百分比 90

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