Analytic Epidemiology - Observational Study Prevalence and Incidence. Flashcards
What is a prevalence rate ?
The proportion of the population that has the disease at a particular time.
Prevalence indicates the probability that a member of the populationhasa given condition at a point in time. It includes all cases who still have the condition and are still members of the population.
What is the equation for prevelance?
π·ππππ π·πππππππππ=(ππ’ππππ ππ πΆππ ππ ππ‘ ππππππ ππππ πππππ‘)/(ππ’ππππ ππ ππππππ ππ ππππ’πππ‘πππ ππ‘ ππππ ππππ πππππ‘)
What is Incidence Risk ?
Risk is a way of quantifying the probability of a particular outcome within a specified period of time.
Risk is the proportion of individuals in a population (initially free of disease) who develop the disease within a specified time interval. Incidence risk is expressed as a percentage (or if small as per 1000 people).
Incidence risk is the total number of new cases divided by the population at risk at the beginning of the observation period
What is the equation for incidence risk ?
Incidence Risk = (ππ’ππππ ππ πππ€ πππ ππ )/(πππ‘ππ ππ’ππππ ππ ππππππ ππ‘ πππ π(πππ πππ π ππππ ππππππ) ππ‘ π‘βπ πππππππππ )
What is the incidence rate ?
Incidence rates also measure the frequency of new cases of disease in a population. However, incidence rates take into account the sum of the time that each person remained under observation and at risk of developing the outcome under investigation.
What is the equation for incidence rate ?
π°ππππ ππππ πΉπππ=(π΅πππππ ππ π΅ππ πͺππππ π πππππ πππππππππ ππππππ )/(π»πππ ππππ ππππππ πππ ππππππππ , ππππππππ πππ πππ ππππππ)
Work out the prevalence
Suppose we were interested in the prevalence of diabetes in a nursing home with 800 residents.
We would begin by doing blood tests on all residents to determine which were diabetic.
If 50 of the residents were found to be diabetic what is the prevelence ?
the prevalence of diabetes at this point in time would be 50/800 = 0.0625.
The standard way of expressing this would be to say that the prevalence was 62.5 per 1000 residents or 6.25 per 100 residents (625 per 10.000), or 0.0625%.
Calculate the incidence risk
In a nursing home with 800 residents.
We would begin by doing blood tests on all residents to determine which were diabetic.50 of the residents were diabetic.
What would be the incidence over the next 12 months if 25 were found to be diabetic the next year ?
If we want to estimate the incidence of diabetes in this population over the next 12 months, we need to exclude the 50 people who are already diabetic (they are not at risk, they are diagnosed) and focus on the 750 residents who are disease-free initially (but are at risk). Assume that all completed the 1 year follow up
We would then need to do additional 750 blood tests after one year to determine how many new cases developed during the span of time.
If 25 were found to be diabetic at the end of a year, then the incidence would be 25/750 = 0.0333 or about 3.3 per 100 (3.3%) over a year.
