Module 2

Question 1

Health measures

Answer 1

a large part of epidemiology involves the use of measures to answer questions about the distribution and determinants of disease
examples = proportion, rate, incidence, prevalence, attack rate

Question 2

Proportion

Answer 2

ratio with no unit of measurement
can be expressed as a decimal, a fraction, or a percentage
A / (A+B)

Question 3

Rate

Answer 3

measures the frequency with which an event occurs in a defined population in a defined time
eg. number of cases of HIV / 10 000 Canadians / year
has dimensions, and has no upper bound

Question 4

Incidence proportion

Answer 4

answers the question = what is the probability that a member of the population will contract this disease within the time-frame?

Question 5

Attack rate

Answer 5

synonym for incidence proportion but used more commonly during outbreaks
outbreak = sudden increase in occurrences of a disease in a particular time and place

Question 6

Incidence rate

Answer 6

incidence rate = incidence density
this results in the number of cases per person-time of observation
allows everyone to contribute time until they experience the event, leave the study, or the year ends event-free

Question 7

Person-time

Answer 7

an estimate of the actual time at risk in years, months, or days that all participants contribute
participants contribute person-time as long as the person is
disease free
still at risk of developing the disease

Question 8

Prevalence

Answer 8

point prevalence = the prevalence of the disease at a certain point in time
period prevalence = the prevalence of the disease within a time period
lifetime prevalence = the proportion of individuals who have had the condition for at least part of their lives at any time during their life course

Question 9

Uses of incidence

Answer 9

expresses the risk of becoming ill, the main measure of acute diseases or conditions, also used for chronic diseases, more useful for studies of causation

Question 10

Relationship between incidence and prevalence

Answer 10

when disease incidence is low, and duration is long, prevalence > incidence
when disease incidence is high, and duration is short, incidence > prevalence

Question 11

Surveillance

Answer 11

ongoing, systematic collection, analysis and interpretation of health data
timely dissemination to persons who need to know
surveillance measures are used to indicate whether something is happening
goal = determine whether anything can be done to prevent the disease or prevent the further spread of disease
this helps public health authorities set priorities

Question 12

Mortality

Answer 12

mortality = a measure of the number of deaths (in general, or due to a specific cause) in a particular population, per unit of time
measuring mortality
the target population of the Death database is deaths of Canadian residents in Canada
the medical certificate of cause of death is completed by the medical doctor in attendance, the coroner, the medical examiner, or other certifier

Question 13

Proportionate mortality and case fatality rate

Answer 13

these values can be calculated for periods less than or greater than 1 year
however, they require mortality and incidence data for these periods
a certain rate over 2 years does not equal to half of the rate over one year
not necessarily equivalent in both years

Question 14

Standardization

Answer 14

used to compare mortality across different populations
for example, we would need to eliminate the effect of age
mortality could be higher in populations with larger proportions of seniors, even if these populations are healthier

Question 15

Direct standardization

Answer 15

start off with absolute mortality rates (crude) based on given information
choose a standard, reference population with known age (and sex) distribution
adjust values by multiplying the crude rates by the weight from the reference population

Question 16

Indirect standardization

Answer 16

used when we don’t have the number of deaths in each age-specific stratum
steps
calculate an expected mortality rate by assuming that the group has similar death rates to the reference population (death rate comes from external data)
compare the observed mortality against the expected

Question 17

Standardized mortality rate

Answer 17

SMR = 100, observed deaths = expected deaths
SMR > 100, observed deaths > expected deaths
SMR < 100, observed deaths < expected deaths

Question 18

Use of prevalence

Answer 18

estimates the probability of the population being ill at the period of time being studied, useful in the study of the burden of chronic diseases and implication for health services