Introduction

For centuries, knowledge about the cause of disease and how to treat or prevent it was limited by the fact that it was based almost entirely on anecdotal evidence. Significant advances occurred when the strategy for studying disease shifted to looking at groups of people and using a numeric approach to make critical comparisons.

Learning Objectives

After successfully completing this section, the student will be able to:

• Define what is meant by the term 'population' in both descriptive epidemiology and analytic epidemiology.
• Explain the difference between fixed versus dynamic populations.
• Explain the differences among the parameters: ratio, proportion, & rate.
• Define and calculate prevalence (and be able to distinguish between point prevalence and period prevalence). Be able to explain the use of prevalence in public health.
• Define and distinguish between cumulative incidence and incidence rate, and describe their strengths and limitations.
• Explain the relationship between incidence rate and cumulative incidence, and be able to compute an estimate of CI from IR.
• Calculate cumulative incidence and incidence rate from raw data and convert it into a form that enables you to compare the incidence in two or more groups.
• Explain what is meant by the term "at risk."
• Explain what is meant by "person-years" of observation and be able to calculate person-years of observation from raw data.
• Explain the interrelationship among prevalence, incidence, and average duration of disease (i.e. P = IR x D). Be able to calculate the average duration of disease, given the prevalence and incidence rate.
• Explain and calculate:

 crude rates

 category-specific rates (e.g. gender or race)

 age-specific rates

• Be able to define and calculate the following special types of frequency measurements:

 morbidity rate

 mortality rate

 case-fatality rate

 attack rate

 live birth rate

 infant mortality rate

 autopsy rate