女性懷孕期間吸菸的嚴重性一直是全球備受關注的議題，吸菸會導致許多嚴重的不良後果，其中雙胞胎胎兒的出生體重受到的影響最大。美國長期來以包裝警語與提高菸稅當作政策工具以抑制百姓吸菸，近年來也採取許多主要減輕二手菸傷害的禁菸政策，譬如公共場所、餐館、酒吧禁菸等。本文主旨是欲探討公共場所禁菸政策等對雙胞胎胎兒出生體重的影響。這是因為公共場所禁菸對胎兒體重之影響尚無定論，而雙胞胎體重比單胞胎體重明顯較輕，身體更加脆弱，更值得關注。
資料係取自2001-2004年美國國家衛生統計中心（National Center for Health Statistics,NCHS）的Natality數據集，在此期間，美國康乃狄克、德拉瓦、佛羅里達、緬因、紐約、南達科他州實施公共場所、餐館以及酒吧禁菸，因此選用此六州的樣本進行分析。
    研究方法為先運用分量迴歸估計各州禁菸政策對胎兒出生體重的影響，由於在不同的分量下胎兒受到的影響有所不同；接著使用兩階段最小平方法，考量到禁菸政策對於母親吸菸的內生性，進而對胎兒出生體重造成影響；最後使用雙重差分法，比較有實施禁菸政策的州與鄰近沒有實施禁菸政策的州進行依自然實驗。
    研究結果顯示，在分量迴歸結果中，禁菸政策導致胎兒出生體重下降，尤其在較輕的分量下，皆為負向且顯著；使用兩階段最小平方法估計，大部分的州在控制時間趨勢下，禁菸政策導致母親每日平均吸菸數量與胎兒出生體重有顯著的負相關，另外，與鄰近的州進行比較，只有佛羅里達與緬因州在特定的分量下，實施禁菸政策的效果正向且顯著。康乃狄克、德拉瓦、佛羅里達之差異中的差異結果顯示均值效果為正向且顯著，這三州控制二手菸的公共場所禁菸等政策對雙胞胎體重的提升呈現有效；惟紐約州均值效果呈負向且顯著，其餘二州不顯著。紐約州中最大都會區--紐約市--是眾所周知工作忙碌的城市，它的獨特性，可能使得立意良善的公共場所禁菸政策得到反向效果。

The relationship between prenatal maternal smoking and its adverse outcomes is well known. Previous studies show that tobacco use during pregnancy is associated with the low birth weight of twins. In recent years, the smoking bans at workplaces, bars or restaurants in the United States have also become increasingly common. We want to know whether smoking bans can improve the birth outcomes of twins since no such study has been done. 
  We use the data from the U.S. National Vital Statistics System, which covers all of the births in the U.S. over the period 2001 to 2004 to test the impacts of smoking bans on the birth weight of twins in Connecticut, Delaware, Florida, Maine, New York, and South Dakota. Only these states in the U.S. implemented smoking bans during that period.
  This study estimates the impacts of birth weight using the quantile regression approach to know how various factors affect different quantiles of the birth weight. Second, we use the two-stage least squares (2SLS) to calculate the impact of smoking on birth outcomes. Third, we use neighboring states as a comparison group and employ a difference-in-difference method to estimate the impact of smoking bans on birth weight.
Our results show that the estimates of smoking bans tend to be negative and significant in lower quantile of the birth weight of twins. The 2SLS estimates of smoking bans are also negative and significant, except for Florida. In contrast, smoking bans are associated with an increase in the birth weight of twins in Delaware, Florida, and Connecticut, compared with neighboring states. However, it is negative and significant in New York. In South Dakota and Maine, they are insignificant. According to the difference-in-difference method, the policy of smoking bans is effective in Delaware, Florida, and Connecticut. It is even worse in New York, which is possibly due to its unique environment.

目錄

第一章 緒論	1
第一節 研究動機	1
第二節 研究目的	5
第二章 文獻回顧	9
第三章 資料來源與變數定義	12
第一節 資料來源與處理	12
第二節 變數定義與敘述統計	14
第四章 實證模型設定	32
第一節 分量迴歸模型	32
第二節 兩階段最小平方法	34
第三節 雙重差分法	35
第五章 實證結果分析	36
第一節 分量迴歸分析	36
第二節 兩階段最小平方法	52
第三節 雙重差分法	54
第六章 結論	63
參考文獻	64
附 錄	66

圖目錄

圖 1 各胞胎出生比例	1
圖 2 禁菸令涵蓋百分比	4
圖 3 美國吸菸率	4
圖 4 各州禁菸政策實施時間圖	6
圖 5 各州相關位置圖	6
圖 6 論文研究架構	8
圖 7 各州胎兒出生體重之趨勢圖	27
圖 8 南達科他與蒙大拿州胎兒出生體重趨勢圖	28
圖 9 德拉瓦與麻里蘭州胎兒出生體重趨勢圖	28
圖 10 佛羅里達與阿拉巴馬州胎兒出生體重趨勢圖	29
圖 11 紐約與新澤西州胎兒出生體重趨勢圖	29
圖 12 康乃狄克與麻薩諸塞州胎兒出生體重趨勢圖	30
圖 13 緬因與新罕布夏州胎兒出生體重趨勢圖	30
圖 14 南達科他州禁菸政策與州稅調整對胎兒出生體重之影響	41
圖 15 德拉瓦州禁菸政策與州稅調整對胎兒出生體重之影響	42
圖 16 佛羅里達州禁菸政策與州稅調整對胎兒出生體重之影響	43
圖 17 紐約州禁菸政策與州稅調整對胎兒出生體重之影響	49
圖 18 康乃狄克州禁菸政策與州稅調整對胎兒出生體重之影響	50
圖 19 緬因州禁菸政策與州稅調整對胎兒出生體重之影響	51
圖 20 南達科他與蒙大拿州政策實施時點	54
圖 21 德拉瓦與馬里蘭州政策實施時點	54
圖 22 佛羅里達與阿拉巴馬州政策實施時點	57
圖 23 紐約與新澤西州政策實施時點	57
圖 24 康乃狄克與麻薩諸塞州政策實施時點	60
圖 25 緬因州政策實施時點	60

表目錄
表 1 變數定義與說明	17
表 2 敘述統計表	19
表 3 南達科他與蒙大拿州之敘述統計	21
表 4 德拉瓦與馬里蘭州之敘述統計	22
表 5 佛羅里達與阿拉巴馬州之敘述統計	23
表 6 紐約與新澤西州之敘述統計	24
表 7 康乃狄克與麻薩諸塞州之敘述統計	25
表 8 緬因與新罕布夏州之敘述統計	26
表 9南達科他州禁菸政策與州稅調整對胎兒出生體重之影響	38
表 10 德拉瓦州禁菸政策與州稅調整對胎兒出生體重之影響	39
表 11 佛羅里達州禁菸政策與州稅調整對胎兒出生體重之影響	40
表 12 紐約州禁菸政策與州稅調整對胎兒出生體重之影響	46
表 13 康乃狄克州禁菸政策與州稅調整對胎兒出生體重之影響	47
表 14 緬因州禁菸政策與州稅調整對胎兒出生體重之影響	48
表 15 各州兩階段最小平方法結果	53
表 16 南達科他州政策實施對胎兒出生體重的影響(對照組：蒙大拿州)	55
表 17 德拉瓦州政策實施對胎兒出生體重的影響(對照組：馬里蘭州)	56
表 18 佛羅里達州政策實施對胎兒出生體重的影響(對照組：阿拉巴馬州)	58
表 19 紐約州政策實施對胎兒出生體重的影響(對照組：新澤西州)	59
表 20 康乃狄克州政策實施對胎兒出生體重的影響(對照組：麻薩諸塞州)	61
表 21 緬因州政策實施對胎兒出生體重的影響(對照組：新罕布夏州)	62

附錄 1 美國各州調稅時間表	66
附錄 2 美國各州禁菸政策實施時間	68
附錄 3 各州第一階段報表	70

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