2. Disease Concepts & Measures of Disease Frequency

Define prevalence

What’s the difference between point prevalence and period prevalence?

Prevalence: measures how common a condition is in a group of people at a certain time

Point prevalence: prevalence of disease at a certain point in time (new and old cases)

Period prevalence: prevalence of disease during a period of time (new and old cases)

How do u calc point prevalence?

What will be the point prevalence of asthma on 31st December 2015 if there are 50 cases of asthma and the population is 1000?

Interpret the answer as well

No. of cases/popn

Answer: 50 existing cases/1000 = 0.05 or 5%
Interpretation: There were 5 cases per 100 people in the popn on 31st Dec 2015

How do u calc period prevalence?

What will be the two-year period prevalence of asthma if there are 50 cases of asthma during 2015, and another 100 during 2016 and the population in 2015 is 1000 and 995 in 2016?

Interpret the answer as well

Total cases/ Average population

• Average population = (population in 1st year + population in 2nd year)/ 2*
  

Answer: 150/(1000 +995/2) x 100 = 15.04% during two years 
Interpretation: There were 15.04 cases of asthma for every 100 people in the population during the two year period

Define incidence

No. of new cases of disease developed in popn in a specific period of time

• It is necessary to follow up disease-free people to measure incidence

Define cumulative incidence