The 18 families selected to be part of the study were then randomly assigned to three groups: 1/3 was invited to participate in NEP-B, 1/3 was invited to participate in NEP-I, and the remaining 1/3 of families was assigned to the control group. The control group remained on a waiting list up until the endline survey was conducted, at which point they became eligible to participate in NEP. Families in the control group receive no NEP benefits, but they continued to receive their usual health care at the health center, which included non-structured talks with the parents and regular control visits to children. Treatment families were free to accept or not the invitation to participate in NEP. We discuss the extent to which they took up this invitation, and the consequences for our estimates.

The final sample includes 162 health clinics stratified by type of health center, 324 facilitators (162 for the basic NEP and 162 for the enhanced NEP-I), and 18 households per health center (6 treatment NEP-B + 6 NEP-I + 6 control), which resulted in a total sample size of 2,916 caregivers and 3,597 children evaluated at baseline.

# 2.3 Measurements

There are two survey waves used in this study: a baseline survey which occurred before the intervention took place, administered in June-September 2011; and an endline survey administered in July-October 2014, almost three years after the end of the group sessions for the sample of households participating in this study. The 6 to 8 week NEP program affecting these households and their children occurred in slightly different periods in each participating clinic, and they all occurred between October 2011 (start date for the first NEP group in the study) and March 2012 (end date for the last NEP group in the study). These surveys cover different dimensions of caregiver characteristics and behaviors as well as child outcomes, which we now describe.

2.3.1 Parental beliefs, attitudes and expectations A set of variables we consider measure different dimensions of parental beliefs, attitudes and expectations. At least one-third of the sessions in NEP aims to promote participants’ self-care and self-image as parents. This dimension of parental, perceptions, related to parental self-efficacy, is grounded in social cognitive theory (Bandura 1986, 1995)). In order to measure this concept, we use the Parenting Sense of Competence Scale (Ohan, Leung, and Johnston 2000), a 17-item scale that evaluates parental confidence in their capacity to overcome daily child-rearing tasks. A complementary instrument captures how parents perceive that their behavior has any impact on child outcomes. To this end, we adopt a subscale of the Parental Cognitions and Conduct Toward the Infant Scale (PACOTIS) (Boivin et al. 2005), a 5-item Likert scale to assess the perceived parental impact of their behavior on the developing child. We dichotomized the items and constructed a perceived impact indicator adding all items.

Social support has been signaled as an important mediator of change in group-based health interventions (Briscoe and Aboud 2012). To measure perceived social support by parents we used a short version of the Social Provision Scale (Cutrona and Troutman 1986), with subscales for perceived support from the family, from friends or the community, and from significant others.

To capture parental beliefs about how to raise children, in particular ideas about structure and warmth in child-rearing tasks, we adapt the Ideas About Parenting (IAP) questionnaire (Heming, 8