A method to assess the environment for genetic studies: the Common Environment Index and the Household Relationships...

Genetic and environmental influences in causing a disease are difficult to measure because of lack of precision in identification of relevant nongenetic variables. The Household Relationships Interview and Schedule was developed to measure shared common environment in families (Common Environment Index) and to take into account developmental stages throughout the life cycle and separation/disruption. Seven trained persons interviewed three individuals who reported fictitious interrelated life histories varying in length and complexity. Discrepancies between the recorded data and the true data were analyzed. Overall 96.1% of the items were recorded correctly. Thus, the method has shown good face and construct validity and reliability for measuring quantity of time shared by relatives in a common household. Common environment as measured by this instrument should be a particularly useful tool in behavior-genetic studies.