Testing hypotheses on specific environmental causal effects on behavior.

Abstract

There have been strong critiques of the notion that environmental influences can have an important effect on psychological functioning. The substance of these criticisms is considered in order to infer the methodological challenges that have to be met. Concepts of cause and of the testing of causal effects are discussed with a particular focus on the need to consider sample selection and the value (and limitations) of longitudinal data. The designs that may be used to test hypotheses on specific environmental risk mechanisms for psychopathology are discussed in relation to a range of adoption strategies, twin designs, various types of "natural experiments," migration designs, the study of secular change, and intervention designs. In each case, consideration is given to the need for samples that "pull-apart" variables that ordinarily go together, specific hypotheses on possible causal processes, and the specification and testing of key assumptions. It is concluded that environmental risk hypotheses can be (and have been) put to the test but that it is usually necessary to use a combination of research strategies.

Childhood adversity and psychosis: Examining whether the association is due to genetic confounding using a monozygotic twin differences approach

“…Because intrapair analyses in MZ twins fully control for genetic influences, any association between the abovementioned variables would be attributable to environmental factors (23, 35) and thus, reject the hypothesis that the association is due to genetic confounding. In the last two analyses each MZ twin pair was the unit of analysis.…”

A Genetically Informed Study of Marital Instability and Its Association With Offspring Psychopathology.

“…This is due to the myriad alternative explanations that can account for the difference between children from divorced and intact families. Given these methodological limitations, Rutter et al (2001) outlined several key needs for the study of environmental causal effects on behavior. In particular, the authors stressed the importance of delineating between alternative hypotheses and using quasi-experimental designs to differentiate between environmental mechanisms from alternative forms of risk mediation, Figure 1 is a graphical representation of how differences in the magnitude of the divorce effect from a few family designs can help account for correlated confounds (see Kendler et al, 1993, for a similar description with a co-twin control design).…”

“…The adoption design is considered to be the strongest test of genetic mediation of intergenerational associations because of the clear separation of genetic and environmental variation. However, the study is limited by the relatively small sample, the weak power to detect differences among families, and the assumption that divorce influences biological and adoptive children similarly (Rutter, Pickles, Murray, & Eaves, 2001). …”

“…However, Meyer et al (2000) reported that the statistical association between marital discord and adolescent conduct problems was mediated by shared genetic factors related to conduct problems in both generations. Extended twin-family studies are able to test both causal and selection processes, but the design includes several major methodological assumptions and restrictions that limit the interpretability and generalizability of the results (D'Onofrio et al, 2003;Rutter et al, 2001). …”

Studying Interactions, Reactions, and Perceptions: Can Genetic Disorders Serve as Behavioral Proxies?

“…For example, in addition to par-against each other two (or more) groups that are similar in certain respects but different in theoretically important ways, mechanisms can be elucidated by which particular outcomes might come about (see Rutter, Pickles, Murray, & Eaves, 2001). …”