Definitions and Equations

Question 1

Exposure AKA risk factor/determinant

Answer 1

any factor that may influence the outcome

Question 2

outcome

Answer 2

the disease, or event or health related state under study

Question 3

prevalence

Answer 3

number of existing cases in a population at a designated time (per 1000)

Question 4

point prevalence

Answer 4

the proportion of persons in a defined population that has the outcome under study at a specific point in time

Question 5

period prevalence

Answer 5

the proportion of persons in a defined population that has the outcome under study over a period of time

Question 6

incidence

Answer 6

number of new cases (per 1000) in a defined period

Question 7

incidence risk

Answer 7

number of new cases in interval/ population initially at risk e.g. mortality rare (static populations)

Question 8

annual incidence

Answer 8

count deaths over calendar year, use mid-year population as denominator, assume population size constant over the year. Expressed as cases per 100,000 per year

Question 9

incidence rate of rare diseases expressed as

Answer 9

per 1,000,000

Question 10

incidence rate of common diseases expressed as

Answer 10

per 1,000

Question 11

cumulative incidence eqn

Answer 11

frequency of new cases over a specified period/ number of people at the start of the period

Question 12

what assumptions does cumulative incidence make

Answer 12

everybody is followed for same length of time
no major changes in death rates

Question 13

what is the benefit of person years incidence over culualtive incidence

Answer 13

it allows for loss to follow up

Question 14

prevalence eqn

Answer 14

Question 15

dependency ratio

Answer 15

the proportion of economically inactive people (due to age)

Question 16

dependency ratio

Answer 16

Question 17

infant mortality rate

Answer 17

(number of deaths of infants aged 0-1 year/number of live births)
for a specific time-period. Reported as infant deaths per 1000

Question 18

under 5 mortality rates

Answer 18

(no. of deaths of infants 0-5 years/no of live births) for a specific time-period. Reported as infant deaths per 1000

Question 19

maternal mortality ration (MMR)

Answer 19

ratio of the number of maternal deaths during a given time period per 100,000 live births during the same time-period

Question 20

fertility rate

Answer 20

• live births per 1,000 women per year
  aged 15 – 44 years
  aged 15 – 49 years (general fertility rate)
• age specific fertility rates

Question 21

total period fertility rate (TPFR)

Answer 21

average number of children that would be born to a woman over her lifetime, assumes that a woman has the same fertility as the population on average and lives beyond the maximum age of giving birth

Question 22

what do different TPFRs indicate

Answer 22

o TPFR > 2.1 population increasing
o TPFR < 2.1 population decreasing

Question 23

life expectancy

Answer 23

• The number of years a baby born today can be expected to live IF it experienced the current age-specific mortality rates
• An average for the whole population – some people will live longer other less

Question 24

life expectancy calculation

Answer 24

Apply age specific mortality rates – 0-1, 1-4, 5-9, 10-14…..50-54…..105-109 – in sequence to a population of 100,000 – add up the total number of years lived / 100,000

Question 25

healthy life expectancy definition and 2 types

Answer 25

• Expected years of life in good or fairly good general health
• Assumes current patterns of mortality and morbidity remain unchanged
• Calculation similar to life expectancy
• Two types
  o life expectancy in good general health
  o disability-free life expectancy (no long term limiting illness)

Question 26

Potential years of life lost (PYLL)

Answer 26

• A measure of the relative impact of various diseases and lethal forces on society.
• Highlights the loss to society from early deaths.

Question 27

PYLL calculation

Answer 27

chose a maximum age and find number of years of life ‘lost when a person dies prematurely
calculate average number lost
all causes of death or specific causes e.g. cardiovascular

Question 28

DALY (disability adjusted life year)

Answer 28

DALY – = years lost (death) plus years spent with disability (allowing for the amount of disability)
* 1 DALY= 1 healthy year of life lost
* Measure of burden of disease – extent to which disease reduces healthy years of life

Question 29

DALY calculation

Answer 29

• Calculated for specific diseases
• Disability plus mortality
• Disability – = incidence x duration x disability
• Mortality – years lost through early death

Question 30

epidemiology definition

Answer 30

The study of the distribution and determinants of health-related states or events (including disease) in a population. Includes identifying risk factors for disease to determine biological pathways and inform healthcare policy

Question 31

descriptive epidemiology

Answer 31

epidemiological studies that focus on the descriptive components rather than analytical components

Question 32

stillbirth rate

Answer 32

the number of stillbirths per 1000 healthy births within a unit of time

Question 33

prevalence

Answer 33

P = I x D