经济激励能提高疫苗接种率吗?——来自诺奖得主的试验设计
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原文信息:Banerjee, A. V., Duflo, E., Glennerster, R., & Kothari, D. (2010). Improving immunisation coverage in rural India: clustered randomised controlled evaluation of immunisation campaigns with and without incentives. BMJ, 340, c2220.
01
引言
方法
02
2.1 抽样
首先,作者在乌代普尔地区随机抽取了134个样本村庄,其中过抽样了远离道路的村庄。为观察干预的溢出效应,还在干预村庄的6公里内随机抽取了一个村庄。
其次,在每个村庄内进行人口普查,将拥有0-5岁儿童的家庭纳入抽样范围。并随机抽取30个家庭作为样本。
该研究的样本对整个乌代普尔地区没有代表性,但对于贫穷区域具有代表性。这些地区的卫生机构具有一个重要特征:卫生人员缺勤严重,疫苗接种服务提供的可靠性较低。
2.2 干预
该文章关注的疫苗是世卫组织(WHO)和联合国儿童基金会(Unicef)所定义的免疫服务包,包括一剂卡介苗(BCG vaccine)、三剂百白破疫苗(DPT vaccine)、三剂口服脊髓灰质炎(小儿麻痹)疫苗(oral polio vaccine)和一剂麻疹疫苗(measles vaccine)。儿童应该在1岁以前接种以上疫苗。
作者开展了两项干预,包括提高疫苗接种服务提供的可靠性和经济激励。
干预A:提供可靠、规律的疫苗接种服务。每个免疫小组包括一个护士和一个助手。该小组在每月的固定日期、固定时段(上午11点-下午2点)在被干预村庄提供服务。另外,每个村庄还有一个社会工作者开展健康教育,宣传接种疫苗的好处。由于Seva Mandir已经在这些地区提供服务多年,当地居民对他们颇为信任。
干预B:在干预A的基础上,还提供经济激励。每次接种疫苗后奖励接种家庭1公斤豆子(价值约40卢比,3/4日薪),在所有疫苗接种完成后奖励一套餐具(75卢比)。
2.3 评估设计
该文章采取聚类随机对照试验设计(clustered randomised control trial)。在抽样到134个村庄后,作者随机选择30个村庄接受干预A,30个接受干预B,其余74个作为对照组。
在控制组中,印度政府和Seva Mandir还在继续提供免费的疫苗接种服务、开展健康教育。
需要说明的是,该实验并没有严格限制儿童的身份。只要儿童的年龄在5岁以下且尚未接种疫苗,不论其来自哪个村庄都可以在Seva Mandir的疫苗接种场所免费接种疫苗;只要儿童年龄在2岁以下,只要其前往干预B所实施的村庄接种点,无论其来自哪个村庄,其父母都可以在疫苗接种后领取豆子。但是,考虑到村庄间距离在20公里以上,有理由认为村庄间不会发生沾染。
2.4 数据收集
在干预开始之前,研究者开发了一个问卷来调查儿童的疫苗接种情况。记录的信息来源包括疫苗接种卡上的记录、父母的回忆、卡介苗疤痕检查等。
基线调查在2004年6月到2005年2月之间开展,调查范围是所有拥有0-5岁儿童的样本家庭。干预在完成基线调查后开始,干预后的调查在2006年7月到2007年2月之间开展,大约是干预计划开始之后的18个月。基线调查和干预后调查的调查员都不知道哪些村庄是干预组。
2.5 统计分析
该研究关注如下几项结果:
(1)是否至少接种了一剂疫苗(不包含口服脊髓灰质炎疫苗,因为几乎所有儿童都接种了此疫苗)。
(2)是否存在卡介苗疤痕。
(3)接种的疫苗总剂数。
(4)完全接种率:是否完全接种了免疫包内的所有疫苗。
除此之外,作者还分析了两种干预的经济成本。
03
结果和结论
Abstract
OBJECTIVE: To assess the efficacy of modest non-financial incentives on immunisation rates in children aged 1-3 and to compare it with the effect of only improving the reliability of the supply of services. DESIGN: Clustered randomised controlled study. SETTING: Rural Rajasthan, India. PARTICIPANTS: 1640 children aged 1-3 at end point. INTERVENTIONS: 134 villages were randomised to one of three groups: a once monthly reliable immunisation camp (intervention A; 379 children from 30 villages); a once monthly reliable immunisation camp with small incentives (raw lentils and metal plates for completed immunisation; intervention B; 382 children from 30 villages), or control (no intervention, 860 children in 74 villages). Surveys were undertaken in randomly selected households at baseline and about 18 months after the interventions started (end point). MAIN OUTCOME MEASURES: Proportion of children aged 1-3 at the end point who were partially or fully immunised. RESULTS: Among children aged 1-3 in the end point survey, rates of full immunisation were 39% (148/382, 95% confidence interval 30% to 47%) for intervention B villages (reliable immunisation with incentives), 18% (68/379, 11% to 23%) for intervention A villages (reliable immunisation without incentives), and 6% (50/860, 3% to 9%) for control villages. The relative risk of complete immunisation for intervention B versus control was 6.7 (4.5 to 8.8) and for intervention B versus intervention A was 2.2 (1.5 to 2.8). Children in areas neighbouring intervention B villages were also more likely to be fully immunised than those from areas neighbouring intervention A villages (1.9, 1.1 to 2.8). The average cost per immunisation was $56 (2202 rupees) in intervention A and $28 (1102 rupees, about pound16 or euro19) in intervention B. CONCLUSIONS: Improving reliability of services improves immunisation rates, but the effect remains modest. Small incentives have large positive impacts on the uptake of immunisation services in resource poor areas and are more cost effective than purely improving supply. TRIAL REGISTRATION: IRSCTN87759937.
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