Understanding Causal Factors Attributing to Risk in Epidemiology - Assignment Example

? Understanding Risk and Causal Factors Attributing to Risk In Epidemiology The was concerned about the concept of relative risk. Risks in epidemiology help to compare disease or events outcome. The various types of risks that are analyzed in epidemiology are: Risk Difference: also known as excess risk is defined as the difference in rates of occurrence between exposed and non exposed groups in the population and is a useful measure of the extent of public health problem caused by the exposure.(Aherns et al,2005) Attributable fraction (exposed): also known as the etiological fraction is defined as the proportion of all cases that can be attributed to a particular exposure. One can determine the attributable fraction by dividing the risk difference by the incidence among the exposed population. These fractions are useful for assessing priorities for public health actions. For example, both smoking and air pollution are the causes of lung cancer but the attributable factor smoking is usually greater than air pollution. (Aherns et al,2005) (Torrence,1997) Population Attributable Risk: is the incidence of disease in a population that is associated with an exposure to a risk factor. This measure is important to determine the relative importance of exposures for the entire population. So it is that proportion by which the incidence rate of the outcome in the entire population would be reduced if exposure were eliminated. It is calculated as difference in the incidence of disease in total population and disease among the exposed group divided by incidence of disease in total population.(Torrence,1997) (Deubner,1998) Relative Risk: this is also called the risk ratio and is the ratio of risk of occurrence of a disease among exposed people to that among the non exposed. The relative risk is thus the ratio of the proportions of cases having a positive outcome in two groups This ratio is a better indicator of the strength of an association than the risk difference since it is expressed relative to the baseline level of occurrence. Thus population with the same risk difference may have different risk ratios depending on the magnitude of the baseline rates. This ratio also is useful to assess the likelihood that an association represents a causal relationship. For instance, the risk of lung cancer in long term heavy smokers compared to non smokers is 22.This is very high and indicates that the relationship is quite high and cannot be considered as a chance finding. (Zhang,1998) (Aherns et al,2005) (Koopman,1999) The relative risk calculations are illustrated below for the incidences of childhood asthma exposed to cigarette smoke and the control group which comprised of children not exposed to cigarette smoke. Positive outcomes (Disease) means asthma and negative outcome (non diseased) means there is no asthma.: Relative risk Top of Form Exposed group Number with positive outcome: a= Number with negative outcome: b= Control group Number with positive outcome: c= Number with negative outcome: d=   Results Relative risk 3.3333 95 % CI 2.5382 to 4.3776 z statistic 8.659 P < 0.0001 Bottom of Form Relative Risk = (a / (a+b)) / (c / (c+d)) Thus from the above example it is clear that the children who are exposed to cigarette smoke are 3.3 times at increased risk to be asthmatics than the non exposed children and the confidence limits of this value ranges from 2.5 to 4.3 times with lower and upper limits of risk and the relative risks are highly significant(p Read More