[Hybrid designs in studies].

The traditional cohort and case-control designs offer a number of advantages but they have several important limitations. There are some alternative study designs for coping with limitations of conventional study designs. These studies are hybrid designs that are economical and efficient in studying risk factors for rare diseases or drug adverse reactions. Hybrid designs are increasingly commonly used in studies. In this paper, hybrid designs including nested case-control, case-cohort, case crossover and case-time control designs were presented.