Allocation designs in cohort and case-control studies.

Four unequal allocation designs for cohort and case-control studies that incorporate cost and power are considered and compared with the equal allocation design, with the aim of providing researchers some flexibility in planning their studies. It is found that the type of design to be adopted depends on available resources and projected needs. In the case of tight expenditure, the minimized cost design is the optimal, whereas the maximized power design may be sought if the researcher intends to ensure a high chance of detecting any clinically significant relative risk of disease.