Wallerstein and Blakeslee (1989) conducted a longitudinal study of 116 children of divorced families. At the time of the first interview, the children's sample was roughly split between eight years old and younger, and nine to eighteen years. The sample was composed largely of Caucasian American (88%), well-educated families in which the divorce had recently occurred. Among a myriad of other findings, data from interviews conducted at five and ten years indicated that divorce had a negative effect on the quality of parent-child relationships. The findings from this study in particular, though, may not represent the experiences of divorced families in general, as the sample was biased toward families who sought clinical help following divorce. Similar results, however, were found by Woodward, Fergusson, and Belsky's (2000) longitudinal investigation, the Christchurch Health and Development Study. The study investigated, from birth through age 16, 1,265 youth of a birth cohort in Christchurch, New Zealand. The researchers found that parental separation was negatively associated with the child's attachment to parents. However, many such studies are countered by the argument that divorce and separation are merely indicators of pre-existing problems--- such as conflict--- in these families, and that these problems, and not the family's structure, cause the negative outcomes in question (Hetherington & Kelly, 2002). Due to this, researchers have had great difficulty trying to prove that the actual process of divorce or the changed family structure, itself, engenders problems in the parent-child relationship. Still, some studies suggest that certain family structures negatively affect elements of the parent-child relationship. Retrospective reports from the cross-sectional, nationally representative National Survey of Families and Households (NSFH) show that, compared to their counterparts from intact families, children in single- or divorced-mother homes spend significantly less time with their residential mother and, especially, with their biological father (Mclanahan & Sandefur, 1994).