in the intervention group there are participants who comply, therefore the average causal effect of assignment to intervention on the actual receipt of services is not zero; and (e) for noncompliers, intervention assignment does not predict outcomes. This last assumption, called the exclusion restriction, is critical because comparing those with longitudinal trajectories similar to those of the interventions families who declined the FCU identifies the latent noncompliers in the control group. In our previous work, we found that parents who decline the FCU are more likely to be less at risk on a variety of factors than are those who engage. Thus, the exclusion restriction bias can be considerably reduced by including covariates in the model that adequately address engagement (Connell, 2009; Jo, 2002b).
