Causal models including genetic factors are important for understanding the presentation mechanisms of complex diseases. Familial aggregation and segregation analyses based on polygenic threshold models have been the primary approach to fitting genetic models to the family data of complex diseases. In the current study, an advanced approach to obtaining appropriate causal models for complex diseases based on the sufficient component cause (SCC) model involving combinations of traditional genetics principles was proposed. The probabilities for the entire population, i.e., normal-normal, normal-disease, and disease-disease, were considered for each model for the appropriate handling of common complex diseases. The causal model in the current study included the genetic effects from single genes involving epistasis, complementary gene interactions, gene-environment interactions, and environmental effects. Bayesian inference using a Markov chain Monte Carlo algorithm (MCMC) was used to assess of the proportions of each component for a given population lifetime incidence. This approach is flexible, allowing both common and rare variants within a gene and across multiple genes. An application to schizophrenia data confirmed the complexity of the causal factors. An analysis of diabetes data demonstrated that environmental factors and geneenvironment interactions are the main causal factors for type II diabetes. The proposed method is effective and useful for identifying causal models, which can accelerate the development of efficient strategies for identifying causal factors of complex diseases.KEYWORDS complex disease; causal model; relative pair; Bayesian Markov chain Monte Carlo (MCMC); population lifetime incidence M OST complex diseases involve a large number of genes and intricate patterns of inheritance. These heterogeneities result in difficulties in identifying genetic models using segregation analyses (Demenais and Elston 1981;Karunaratne and Elston 1998; SAGE 1994). The flexible framework based on variance components has enabled many extensions for fitting genetic models, with major causal factors of additive genetic effects, shared environment, and unique environment (Morton and MacLean 1974;Falconer and Mackay 1996;Rabe-Hesketh et al. 2008). Genetic models based on familial aggregation using relative risk and covariance could provide partial assessment of relevant parameters such as the number of loci and/or the disease allele frequencies (Elston and Campbell 1970;McGue et al. 1983;Risch 1990;Lange 2002;Slatkin 2008).These genetic models are based on linear models that search the linear relationships between the trait and the causal components. The linear models in genetics were developed to be applicable to most kinds of genetics problems (Mackay 2014). While genetic epidemiologists have focused on the development of modern statistical technologies derived from Fisher's variance components (Fisher 1918), the focus of epidemiologists has been the fundamental concept of causation. A cause is an even...