Through the analysis of Rayleigh model, an explanatory model for the quality effect of peer reviews is constructed. The review activities are evaluated by the defect removal rate at each phase. We made hypotheses on how these measurements are related to the product quality. These hypotheses are verified through regression analysis of actual project data, and concrete calculation formulae are obtained as a model. Making use of the mechanism to construct this model, we can develop a method for making concrete review plan and setting objective values to manage on-going review activities.