198 In case-control study design (Fig. 7. 4), the study populatio n's disease status will be ascertained first. Those with the disease are considered as coses and those who do not have the disease are considered in the control group. The p1·esence of the suspected el\. l)Osurc factor for both groups will then be determined. The incidence or prevalence rate can not be computed in case-control study design; hence, the odds ratio will be the measure of disease association. lnterventional or Experimental Epidemiology Ioterventiona l Epidemiology aims to test effectiveness or ""reasonableness" of intervention programs designed to prevent and control diseases utilizing randomjzed controlled or clinical trials, field or community trials. Evaluation Epidemiology Evaluation Epidemiology attempts to measure the effectiveness of different health services and intervention programs. The app Jication of epiclemio ]ogical methods in evaluating programs to control and prevent epidemics of communicable diseases led to global efforts in eradicating cliseases like polio or thwart transmission of diseases to pandemic proportion. (Beagle hole et al, 1993) 