The nm·se characterizes the pattern of disease occurrence in terms of date or time onset. This is indicated by the epidemic or attaek curve. Disease occurrence can be described by the following: 1. Short time fluctuations common in epidemics: a. Common source epidemic is cliaracterized by simultaneous exposure of a large number of susceptible to a common infectious agent; b. Propagated epidemic is caused by a person-to-person transn1ission of disease agent; 2. Cyclic variation refers to recurrent fluchlations of disease that may ex. hibit cycles la,;ting for certai o 1>eriods; 3. Secular variation refers to changes in disease freque11cy over a perio. d of many years. The demonstration of association of a disease with place implies either t J1at t J1e people living in a certain geographical location have certain traits or are uni([nely different from those residing in other places. The differences in terms of traits may have been influenced by certain environ. menta l factors present in tlle biologic, chemica J, physical or social environments of the people inhabiting that place. 3. Analysis of the general pattern of occurrence of the disease or condition After establishing the disease frequency and distribution in a population and defining the characteristics of the d. isease or condition in relation to time, place and person, the nurse proceeds to correlate the data and attempts to formulate. a causal association between the disease under shldy an·d the probable factors surrounding it. It focuses on clinical observations using case reports or case series. This stage is called hypothesis testing. The exposure factors and the disease wi. U be tested or proven in the next phase of the epidemiological process. Analytical Epidemiology More than just describing the disease in terms of person, place and time, Analytical Epidemiology attempts to identify the possible factors as&oc;iated with disease oc. currence. Using the concepts of causality and association, it seeks to establish the risk of developing specific disease or condition among people exposed to known factors or situal'ions. It consists of hypothesis-testing of causal association using different epidemiological study designs. Case-contro l and cohort studies are employed in investigating patterns of disease and cause in individuals. Correlational or ecologic studies are utilized in analyzing patterns of dis-ease and cat1se in populations. Analytic studies employ measures that show strength of association between a purported health condition or factor to increase risk of disease. These measures, a. lso called risk estimates a. re relative risk ratio (RRR), odds ratio (OR) and attributable risk (AR). Risk Estimates The relative risk to an individual developing a disease due to a particular exposure is derived by comparing the occurrence of a disease in a population exposed to the suspected factor to u,e occurrence of disease in a population not exposed to the suspected factor. It is a direct measure of the strength of associatio n between a suspected cause and effect (Lilienfeld et al, 1994) The relative risk ratio only implies an increased probitbility of developing a disease as a result of exposure to a risk factor. A relative risk ratio of 1. 0 means that the ris. k is the same for botl1 exposed and non­ exposed populations. A risk greater than 1. 0 indicates excess risk in the exposed group. (Valaois, 1992) 195 