Definitions and Equations Flashcards
Exposure AKA risk factor/determinant
any factor that may influence the outcome
outcome
the disease, or event or health related state under study
prevalence
number of existing cases in a population at a designated time (per 1000)
point prevalence
the proportion of persons in a defined population that has the outcome under study at a specific point in time
period prevalence
the proportion of persons in a defined population that has the outcome under study over a period of time
incidence
number of new cases (per 1000) in a defined period
incidence risk
number of new cases in interval/ population initially at risk e.g. mortality rare (static populations)
annual incidence
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
incidence rate of rare diseases expressed as
per 1,000,000
incidence rate of common diseases expressed as
per 1,000
cumulative incidence eqn
frequency of new cases over a specified period/ number of people at the start of the period
what assumptions does cumulative incidence make
everybody is followed for same length of time
no major changes in death rates
what is the benefit of person years incidence over culualtive incidence
it allows for loss to follow up
prevalence eqn
dependency ratio
the proportion of economically inactive people (due to age)
dependency ratio
infant mortality rate
(number of deaths of infants aged 0-1 year/number of live births)
for a specific time-period. Reported as infant deaths per 1000
under 5 mortality rates
(no. of deaths of infants 0-5 years/no of live births) for a specific time-period. Reported as infant deaths per 1000
maternal mortality ration (MMR)
ratio of the number of maternal deaths during a given time period per 100,000 live births during the same time-period
fertility rate
- live births per 1,000 women per year
aged 15 – 44 years
aged 15 – 49 years (general fertility rate) - age specific fertility rates
total period fertility rate (TPFR)
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
what do different TPFRs indicate
o TPFR > 2.1 population increasing
o TPFR < 2.1 population decreasing
life expectancy
- 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
life expectancy calculation
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
healthy life expectancy definition and 2 types
- 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)
Potential years of life lost (PYLL)
- A measure of the relative impact of various diseases and lethal forces on society.
- Highlights the loss to society from early deaths.
PYLL calculation
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
DALY (disability adjusted life year)
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
DALY calculation
- Calculated for specific diseases
- Disability plus mortality
- Disability – = incidence x duration x disability
- Mortality – years lost through early death
epidemiology definition
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
descriptive epidemiology
epidemiological studies that focus on the descriptive components rather than analytical components
stillbirth rate
the number of stillbirths per 1000 healthy births within a unit of time
prevalence
P = I x D
