Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, USA.
Division of Health Policy and Management, College of Health Sciences, Korea University, Seoul, South Korea.
Sci Rep. 2022 Apr 19;12(1):6411. doi: 10.1038/s41598-022-10192-1.
Head Start is a federally funded, nation-wide program in the U.S. for enhancing school readiness of children aged 3-5 from low-income families. Understanding heterogeneity in treatment effects (HTE) is an important task when evaluating programs, but most attempts to explore HTE in Head Start have been limited to subgroup analyses that rely on average treatment effects by subgroups. This study applies an extension of multilevel modelling, complex variance modelling, to data from a randomized controlled trial of Head Start, Head Start Impact Study (HSIS). The treatment effects on the variance, in addition to the mean, of nine cognitive and social-emotional outcomes were assessed for 4,442 children aged 3-4 years who were followed until their 3rd grade year. Head Start had positive short-term effects on the means of multiple cognitive outcomes while having no effect on the means of social-emotional outcomes. Head Start reduced the variances of multiple cognitive and one social-emotional outcomes, meaning that substantial HTE exists. In particular, the increased mean and decreased variance reflect the ability of Head Start to improve the outcomes and reduce their variability. Exploratory secondary analyses suggested that larger benefits for children with Spanish as a primary language and low parental educational level partly explained the reduced variability, but the HTE remained and the variability was reduced even within these subgroups. Routinely monitoring the treatment effects on the variance, in addition to the mean, would lead to a more comprehensive program evaluation that describes how a program performs on average and on the entire distribution.
“Head Start”是美国一个为来自低收入家庭的 3-5 岁儿童提供的、由联邦政府资助的全国性项目，旨在提高他们的入学准备水平。在评估项目时，了解处理效果的异质性（HTE）是一项重要任务，但大多数探索“Head Start”中 HTE 的尝试都仅限于基于子组的平均处理效果的子组分析。本研究应用了多层次建模、复杂方差建模的扩展，对“Head Start”的一项随机对照试验——“Head Start 影响研究（HSIS）”的数据进行了分析。对 4442 名 3-4 岁儿童的 9 项认知和社会情感结果的方差和均值进行了评估，这些儿童一直随访到他们的三年级。“Head Start”对多项认知结果的均值有短期的积极影响，而对社会情感结果的均值没有影响。“Head Start”降低了多项认知和一项社会情感结果的方差，这意味着存在大量的 HTE。特别是，均值的增加和方差的降低反映了“Head Start”提高了结果并降低了它们的可变性的能力。探索性的二次分析表明，对于以西班牙语为主要语言和父母教育程度较低的儿童来说，更大的收益在一定程度上解释了方差的降低，但 HTE 仍然存在，即使在这些子组内，方差也有所降低。常规监测处理效果的方差，除了均值，将导致更全面的项目评估，描述一个项目的平均表现和整个分布。
