Introduction to Epidemiology Investigation

Question 1

Define prevalence

Answer 1

Measuring existing cases – unit % - counts people

Question 2

How is prevalence calculated?

Answer 2

Incidence x duration of disease

Question 3

What incidence rate?

Answer 3

Measuring new cases – counts cases in certain amount of people over period counted

Question 4

How is incidence calculated?

Answer 4

Incidence rate = new events / (person x time (years)) = events per person per time (yr)

Question 5

What is person-years?

Answer 5

Sum of the total time of everybody followed up in a study

Question 6

What is tendency vs observation?

Answer 6

T = likelihood of occurrence.

O = observed cases

Question 7

What is a hypothesis?

Answer 7

A statement that an underlying tendency of scientific interest takes a particular quantitative value

Question 8

What is the p-value?

Answer 8

<0.05 = reasonable to reject the stated hypothesis, observations are statistically significant

> 0.05 = fail to reject the hypothesis

Question 9

What is a null hypothesis?

Answer 9

Hypothesis: no better or worse, same (ratio of rates) = 1

Hypothesis: no more or less (difference between) = 0

null hypothesis value inside 95% CI —> p ≥ 0.05 FAIL TO REJECT

null hypothesis value outside 95% CI —> p < 0.05 REJECT

Question 10

How are the confidence intervals calculated?

Answer 10

lower bound = value / error factor

upper bound = value x error factor

Question 11

How are the error factors calculated?

Answer 11

For incidence rates = e^2√ (1÷d) - where d is events observed in a population

For prevalence = e^2√ (1÷d) - where d is events observed in a population

For incidence rate ratio = e^2√ (1÷d(1) + 1÷ d(2)) - where d cases in each population respectively

For standardized mortality rate = e^2√ (1÷O) - where O is observed number of events in pop