Epidemiology

Basic Concepts

The following are basic concepts in epidemiology: Probability provides the foundation for statistical inference.

Statistical inference draws conclusions about an entire population based on a sample from that population.

Statistical data are understood better when graphical representation is used, because visual presentation helps to identify variations and examine the shape of the distribution. A histogram is used to demonstrate a graph of a frequency distribution.

Frequency distribution has certain characteristics; data may show a central tendency or variation (dispersion).

Average and median are measures of central tendency, whereas range, variance, and standard error are measures of dispersion or variation. Given a set of n measurements normally distributed, on average 68.3% of measurements are within 1 standard deviation of the mean, 95.5% are within two standard deviations of the mean, and 99.7% of measurements are within 3 standard deviations of the mean.

Proportion measures relate the number of events occurring in a given place at a given time with a reference population.

Prevalence, the number of existing cases of a disease, is used with chronic diseases and those of long duration.

Incidence, the number of new cases over a specific period of time, is used mainly with infectious diseases and those of short duration.

Ratios are measures that relate two events in different populations and areas, such as mortality ratio.

Rates, in epidemiology, are incidence density measures, where the numerator is the number of new cases and the denominator is person-time (i.e., per person per time period).

Applications

The study of the distribution of diseases began with the analysis of the causes of infectious diseases and actually involves the study of the distribution of all diseases. [Page 188]Lifestyle, environmental or toxic exposures, and even bioterrorism are factors well documented in modern epidemiological studies.

The analysis of risk factors and relative risks ratios are important measurements in the study of the distribution of diseases. The risk for heart disease is increased in people who have high cholesterol and also in people with arterial hypertension but is further increased for a person who has the two risk factors, high cholesterol and high blood pressure, at the same time. Against this background of basic information, this section seeks to explain the significance of what it means to properly implement epidemiological findings. Epidemiology in a pure sense has been reserved as a science for people with special mathematical training and knowledge but with limited impact on decision making. It is thus explainable why we accumulate important information that frequently is missed when managers and government officers in the health care industry implement public health strategies.

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