Intro. to Epidemiology Flashcards
What are the two assumptions epidemiology makes?
Human disease does not occur at random
Has causal and preventative factors that can be investigated through systemic investigations of different populations
What males Epidemiology unique?
Studies are conducted on human populations rather than laboratory or animal research
How do you calculate prevalence?
[Number of people with disease] / [ Total number of people]
How do you calculate incidence?
[New cases during study period] / [Total population at risk]
In the previous example, consider the situation where the same 500 participants were
recruited in the study and after a follow-up period of 6 months, a total of 30 TB cases
were identified [12 cases on 30th Marth, 8 cases on 17th June and 10 cases on 29th
July]. Information gathered at baseline indicated that 20 of the recruited participants
had been vaccinated against TB.
• What would be the incidence of TB in the study period expessed as % per year?
• New cases in study period: 30 in total
• Population at risk at baseline: 500 – 20 (vaccinated) = 480
participants
• In 6 months: Incidence = (30/480) x 100/6 months = 6.25 %/6
months
à Annual incidence = 6.25 x 2 = 12.50 %/year
What factors affect the incidence density?
Beginning with a disease free population (meaning those diagnosed at the start are disregarded)
People who left the study
Patients diagnosed
People who stayed
Numerator and denominator of incidence density
Numerator: number of cases of disease during specified time interval
Denominator: summed person-years (p x t)
Where p is the person
and t is the time that person was observed during the study
How do we calculate food specific incidence rate?
[Cases of illness in people who ate a food] / [Total number of people who ate the same food]
How are incidence and prevalence related?
Prevalence = incidence x Average duration of disease
Ex.
If prevalence increases, and incidence does not change, the duration of disease increases to restore the
balance.
If incidence increases, and prevalence does not change, the duration of disease decreases to restore
the balance.
How do we calculate annual mortality rate?
[Total deaths (from all causes) in one year] / [Total population at MID YEAR]
Mid year is used because population may change for a lot of reasons, mainly migration
What is maternal mortality rate?
[Number of maternal deaths] / [Number of live births]
Infant mortality rate?
Total number of infant deaths (<1 year old) PER 1000 live births
Child under 5 mortality rate?
Total number of children deaths (<5 years old) PER 1000 live births
How do we calculate proportionate mortality?
Ratio of measured death from one cause vs others
Ex. Proportionate mortality from diarrhea
[deaths from diarrhea] / [total deaths in south asia]
If we add up all proportionate mortality for all disease
conditions, we should get 100%
