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2 weeks ago
compare and contrast an epidemiological study for an acute health problem with a long-term epidemiological study.
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2 weeks ago
Hi bsnready

This is tough question to answer, though I found a source that may shed some light.


A fundamental concept that underpins all epidemiological research is the requirement for clearly defining the source population, also known as the study base. In studies of occupational risk factors for disease and injuries, the source population should be a cohort of workers from one or more industries. Identifying the source population is relatively straightforward when conducting a study of a well‐defined cohort of workers from a particular industry or facility, as is typical of most occupational cohort mortality studies. Less well appreciated is that a study that focuses on a certain health outcome, and seeks to identify multiple possible occupational risk factors, such as a population‐based case‐control study, has an implicit source population that generated the cases, namely the general population that includes workers from the industries and occupations of interest, workers from other industries, and non‐employed persons. For example, consider a community‐based case‐control study of occupational risk factors for Parkinson's disease in which associations are estimated for employment in various occupations, such as farming, welding, and teaching, as well as associations with certain exposures that may span numerous occupations, such as pesticides, metals and infectious agents. In this situation, the source population would include a number of different subpopulations defined by occupation (farmers, welders, teachers) or by exposure (pesticides, metals, infectious agents). An underlying validity principle is that the controls' exposures in the case‐control study should represent the exposure experience of the source population.

A second important point is that the new occurrence of disease, incidence, is the basic measure of disease occurrence that epidemiologists seek to estimate. Measuring new onset of illness or injury is largely unambiguous for acute health outcomes, such as non‐fatal workplace injuries. Mortality is a special type of incidence in which the “event” is death rather than the occurrence of (non‐fatal) disease or injury. It therefore is often used as a surrogate for disease incidence for diseases that are usually fatal (for example, cancer), but may also be affected by factors that affect survival as well as risk factors for disease incidence. Determining disease incidence is especially challenging for conditions that do not have sharp times of onset, even when serial health measurements are made. Coal worker's pneumoconiosis is a disease that fits this description. Many health outcomes develop over prolonged time periods in which onset times can only be inferred from indirect evidence. This is the case for conditions such as chronic obstructive lung disease, but is also true for diseases such as cancer for which there is generally a single diagnostic point in time, but the underlying disease process may have developed over many years. It should also be appreciated that chronic disease onset times are typically classified as single events, such as dates of disease diagnosis or death, although true disease onset is a continuous phenomenon that is difficult to characterise epidemiologically.

In certain situations (for example, cognitive impairment), determining the onset of incident disease may be impractical, and thus disease prevalence is studied instead. Although disease prevalence may be a surrogate for incidence, it is also affected by factors that determine the duration of disease (including factors that affect survival or treatment efficacy) in addition to risk factors for disease incidence. This is not to say that studies based on prevalence are inherently flawed or invalid, although distinguishing associations of health outcomes with occupational exposures that pertain to disease aetiology from those that may be related to disease severity, prognosis and duration can be difficult, if not impossible, when prevalent cases are included in a study.
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