What is the Difference Between Incidence and Prevalence

The main difference between incidence and prevalence is that incidence is the number of new occurrences of a particular disease in the population over a period of time, whereas prevalence is the number of cases of a particular disease in a certain population over a period of time. Furthermore, incidence gives the rate of manifestation of a disease in a particular population, while prevalence describes how widespread the disease is. 

Incidence and prevalence are two epidemiological measurements that measure the probability of occurrence of a particular disease in a particular population. Out of these two, incidence is the more correct measurement that determines the risk of a disease of a particular population. 

Key Areas Covered 

1. What is the Incidence
     – Definition, Measurement, Importance
2. What is Prevalence
     – Definition, Measurement, Importance
3. What are the Similarities Between Incidence and Prevalence
     – Outline of Common Features
4. What is the Difference Between Incidence and Prevalence
     – Comparison of Key Differences

Key Terms 

Disease Occurrence, Epidemiology, Incidence, Period Prevalence, Population Prevalence, Prevalence

What is the Incidence 

Incidence is the number of new occurrences of a particular disease in a population over a period of time. Therefore, it gives the rate of new diseases. More meaningfully, the incidence rate can be reported as a fraction of the population at risk; for example, per million population.

Figure 1: Breast Cancer Incidence by Age in Women in the UK 2006-2008

However, the accuracy of the incidence data depends on the accuracy of the diagnosis of the disease. Furthermore, the incidence rate can be given based on the different subsets of the population, such as gender, age, racial origin, diagnostic category, etc.

What is Prevalence 

Prevalence is the number of individuals in a population with a particular disease condition. Therefore, it includes both new and old cases of the disease. Moreover, there are two types of prevalence: point prevalence and period prevalence. 

Figure 2: Total Number of New HIV Infections and AIDS Death for each Year between 1986 and 2010 Reported in Malaysia, by Gender

Basically, point prevalence is the prevalence at a given point of time. In contrast, period prevalence is the prevalence over a period of time. However, period prevalence is widely used and the most suitable form of measurement. On the other hand, prevalence can be more meaningfully interpreted as the number of cases as a fraction of the total population at risk. Furthermore, it can be further divided into different subsets as in incidence.

Similarities Between Incidence and Prevalence 

• Incidence and prevalence are two measurements of epidemiology. 
• They help to determine the probability of occurrence of a particular disease in a particular population. 
• Also, both measurements take into account the new cases of that particular disease. 
• Moreover, they are important in the studies of public health. 

Difference Between Incidence and Prevalence 

Definition 

Incidence refers to a measurement of the probability of occurrence of a given medical condition in a population within a specified period of time, while prevalence refers to the portion of a particular population found to be affected by a medical condition over a period of time. Thus, this is the main difference between incidence and prevalence.

Type Cases 

Moreover, incidence only takes new cases of the disease into account in the population, while prevalence takes both old and new cases into account in the population. 

Denominator 

The denominator of incidence is the population at-risk, while the denominator of prevalence is the whole population. 

Follow-up of Individuals 

Further, incidence requires the follow-up of individuals in a population to identify new cases, while prevalence does not require such follow-up of individuals to identify cases. 

Duration of Disease 

Also, another difference between incidence and prevalence is that incidence does not depend on the duration of illness, while prevalence depends on the duration of disease. 

Significance 

Incidence measures the rapidity of disease occurrence, while prevalence measures the proportion of the population with disease. 

Preferred with 

Besides, incidence is preferred when studying cause and effect, while prevalence is preferred when estimating the population-based burden of a chronic disease or attribute. 

Importance 

Furthermore, incidence is the more reliable measurement in determining the risk of a certain disease to the population while prevalence indicates how widespread the disease. 

Conclusion 

Incidence is the number of new cases of a particular disease in a population over a period of time. Therefore, it allows determining the rapidity of disease occurrence of a disease. It is also important to determine the risk of a certain disease. On the other hand, prevalence is the number of both new and old cases of a particular disease in a population. Therefore, it measures the number of individuals with the disease in the population. Furthermore, it indicates how widespread the disease is in the population. However, the main difference between incidence and prevalence is the type of measurement. 

References:

1. “Incidence and Prevalence: Key Epidemiological Concepts.”European Patients’ Academy, EUPATI, 3 Mar. 2018, Available Here.

Image Courtesy:

1. “Breast cancer incidence by age in women in the UK 2006-2008” By Mikael Häggström – Own work (CC0) via Commons Wikimedia   
2. “NO. OF NEW HIV INFECTIONS AND AIDS DEATHS BY GENDER PER YEAR REPORTED IN MALAYSIA (from 1986 until 2010)” By Benjy8769 – Own work (CC BY-SA 4.0) via Commons Wikimedia