What is the difference between incidence and prevalence

Notable examples of this include incidence and prevalence. Often these words are used interchangeably however, when it comes to surveillance and epidemiological analyses these words have both distinct meanings and purpose.

To help understand the difference between incidence and prevalence, epidemiologists often refer to the familiar concept of water entering and leaving a bath.

The prevalence is the number of individuals with the disease either at a specific point in time the point prevalence or over a specified time period the period prevalence. The key concept about the prevalence is that it includes both new and existing cases of disease.

If we refer to our bathtub, the prevalence is the amount of water in the bathtub at a specified point in time. As we all know, this quantity is not static and we can easily add more water, by turning on the tap, as well as lose water through evaporation or by opening the plug. Turning back to our disease model, the filled bath represents the total number of cases at a point in time which can change through evaporation or releasing the plug as individuals recover from the disease or if they unfortunately pass away.

Therefore, the prevalence of a disease in a population is influenced by a number of parameters: the number of new cases turning on the tap , the speed of recovery — which is influenced by disease severity and treatment options evaporation and the number of people that lose their lives to the disease releasing the plug. The same assumption is made for participants diagnosed with the disease at the year 2 examination — some may have developed illness in month 1, and others in months 2 through So, on average, they developed illness halfway through the year.

The denominator of the person-time rate is the sum of all of the person-years for each study participant. So, someone lost to follow-up in year 3, and someone diagnosed with the disease in year 3, each contributes 2. Example A: Investigators enrolled 2, women in a study and followed them annually for four years to determine the incidence rate of heart disease. After one year, none had a new diagnosis of heart disease, but had been lost to follow-up.

After two years, one had a new diagnosis of heart disease, and another 99 had been lost to follow-up. After three years, another seven had new diagnoses of heart disease, and had been lost to follow-up. After four years, another 8 had new diagnoses with heart disease, and more had been lost to follow-up. The study results could also be described as follows: No heart disease was diagnosed at the first year. Heart disease was diagnosed in one woman at the second year, in seven women at the third year, and in eight women at the fourth year of follow-up.

One hundred women were lost to follow-up by the first year, another 99 were lost to follow-up after two years, another were lost to follow-up after three years, and another women were lost to follow-up after 4 years, leaving women who were followed for four years and remained disease free. Calculate the incidence rate of heart disease among this cohort. The incidence proportion underestimates the true rate because it ignores persons lost to follow-up, and assumes that they remained disease-free for all four years.

Example B: The diabetes follow-up study included diabetic women and 3, nondiabetic women. By the end of the study, 72 of the diabetic women and of the nondiabetic women had died. The diabetic women were observed for a total of 1, person years; the nondiabetic women were observed for a total of 36, person years. Calculate the incidence rates of death for the diabetic and non-diabetic women. Prevalence, sometimes referred to as prevalence rate , is the proportion of persons in a population who have a particular disease or attribute at a specified point in time or over a specified period of time.

Prevalence differs from incidence in that prevalence includes all cases, both new and preexisting, in the population at the specified time, whereas incidence is limited to new cases only.

Point prevalence refers to the prevalence measured at a particular point in time. It is the proportion of persons with a particular disease or attribute on a particular date.

Period prevalence refers to prevalence measured over an interval of time. It is the proportion of persons with a particular disease or attribute at any time during the interval.

The value of 10 n is usually 1 or for common attributes. The value of 10 n might be 1,, ,, or even 1,, for rare attributes and for most diseases.

In a survey of 1, women who gave birth in Maine in , a total of reported taking a multivitamin at least 4 times a week during the month before becoming pregnant.

Figure 3. Each horizontal line represents one person. PD is a lifelong and progressive disease, which means that symptoms slowly worsen over time. Prevalence: the number of people in a population who have a disease or other health outcome at one point in time. Fox Foundation. Prevalence helps us understand how many people are currently living with this condition, and it also helps researchers find patterns among different groups of people.

Is it more prevalent among men or women? With this information, researchers can now devote more time to find out how. Gathering prevalence data is a vital first step to better understanding who develops PD and why. However, PD is hard to diagnose, so prevalence data are often undercounted. However, we can approximate the number based on representative samples. Some estimates even put PD prevalence at more than 10 million people. Difference Between Similar Terms and Objects. MLA 8 M, Emelda.

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