As can be seen in the Table 5, cases had higher odds than controls to be exposed to residential radon gas in excess of 200 bcq per cubic metres. In this case, Odds Ratios are relative risk estimates of the association between exposure and outcomes. In this case, we can state that Radon gas is a risk factor for lung cancer with a relative risk estimate of 2.15, this is a crude Odds Ratio. We use the Odds Ratio in this situation as we would use the RR and we can calculate the reduction in lung cancer prevalence if we were to reduce the exposure to Radon gas to zero.
Epidemiological Study Designs
These different measures of association are obtained on the basis of epidemiological studies. In environmental and occupational epidemiology, we do not test the results of interventions as Environment is the source of exposure. Hence, we conduct different types of epidemiological studies: ecological studies (secondary data analyses from primary data), case control studies either by themselves or case control studies that are nested within cohort studies, and cohort studies.
Ecological studies are those where data in aggregated forms are correlated. This is in the form of regression analyses or testing of linear models. Imagine you want to test your theory that Air Pollution causes Asthma. You would test your hypotheses that those who are exposed to poor air quality are more likely to get admitted to hospitals with Asthma related issues, or if nothing, Asthma symptoms would worsen during periods of poor air quality. In order to test this hypothesis, you would set up a study where you would correlate air quality indicators and rate or likelihood of hospital admissions with Asthma and related symptoms.
Ecological studies are useful for being relatively inexpensive but they cannot provide definite information about causes and effects. This is because while they are useful for population based aggregated associations, the results from ecological studies cannot be extended to individuals. For example, while using Air quality data and aggregated hospital admissions, one can state that poor air quality is a risk factor for Asthma related hospital admissions, it does not follow that every time there is a drop in the air quality, an individual residing in the area where the air quality worsened would be at higher risk of hospital admission. This is referred to as
ecological fallacy.