Week 1 Flashcards
exposure
(risk factor or determinant)
any factor that may influence the outcome
outcome
the disease, or event, or health related state under study
define epidemiology
the study of the distribution/frequency of health related states and determinants in a population
assumptions in epidemiology
disease does not occur at random
disease has casual and preventative factors
role of epidemiology
to describe patterns of health and disease within populations
to interpret these differences
to apply results to public health practice
to evaluate effect of health-related interventions
observational epidemiology
describes patterns of health and disease without intervening to change the factors which influence them
what do descriptive studies measure
burden of illness
examples of descriptive studies
analytical study
can investigate risk factors for a disease or outcome (does not necessarily mean they are casual)
interventional epidemiology
assess effect of a specific intervention
individual level or community
case definition
method used to identify a case
boundaries of cases
unit analysis
prevalence
number of existing cases in a population at a designated time
the number of affected persons present in the population divided by the number of people in the population
prevalence calculation
no. of cases (people with disease)/
no. of people in the population
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
when would you use period prevalence
measuring episodic conditions
what is prevalence useful for
useful for assessing the burden of disease within a population
valuable for planning
what is prevalence not useful for
determining what causes disease
2 measures of incidence
risk and rate
incidence risk
number of new cases in interval over the population initially at risk (mortality rates)
incidence rate
number of new cases/ total person-time at risk
when to use incidence risk
good for static populations
when to use incidence rate
dynamic populations
annual incidence
count deaths over calendar year (from routine data)
- use mid-year population as denominator
- expressed as cases per ….
cumulative incidence
frequency of new cases over a specified period
denominator is no. of people at the start of the period
(events divided by initial population)
potential problems with cumulative incidence
loss to follow up
person years at risk
say there was 500 women being followed up over 2 years
500 for year 1
and say 300 died so for year 2 there was only 200 left
200 for year 2
total= 700
allows for loss to follow up
what does annual incidence tell us
number of new cases over defined period
sensitive to changes in disease risk
more suitable for monitoring trends
less suitable for assessing burden of disease
incidence vs prevalence
number of new cases vs number of existing cases
age specific death rate
no. of people (in age group)
prevalence in relation to incidence
prevalence = incidence x average disease duration
P= I x D
