Define epidemiology
the study of populations in order to determine the frequency and distribution of disease
What is the point of epidemiology
- to identify risk factors for disease
- to determine optimal treatment approaches to clinical practice and preventive medicine
What is one of the first recorded examples of epidemiology to investigate and manage outbreak of infectious disease
John snow - broad street pump, cholera epidemic, london, 1854
What are the major roles of epidemiology
- Monitor infectious and non-infectious diseases
- Study natural history of diseases
- Investigation of disease risk factors
- Health care needs assessment
- Development of preventive programmes
- Evaluation of interventions
- Health Service planning
What are the 3 main types of epidemiology study
- descriptive (observational)
- analytic (observational)
- intervention (experimental)
What are the measures of disease frequency used in descriptive epidemiology
- Prevalence
- Incidence
Define prevalence
a measurement of all individuals affected by the disease within a particular period of time or point in time
How do you work out prevalence
number of affected individuals divided by total number of persons in population
What kind of studies are used to find prevalence
cross-sectional studies or from registers
Define incidence
a measurement of the number of new individuals who contract a disease during a particular period of time
What kind of studies are used to find incidence
longitudinal studies or from registers
What is the key difference between prevalence and incidence
Prevalence: at a point in time
Incidence: over a period of time
When would you use prevalence or incidence? give examples
Generally:
Chronic diseases = prevalence (apart from cancer = incidence)
Acute diseases = incidence
is the common cold likely to have a high or low incidence and prevalence? Why?
(a short duration curable condition) = high incidence but low prevalence
because many people get a cold each year, but few people actually have a cold at any give time (so prevalence is low)
is diabetes likely to have a high or low incidence and prevalence? Why?
(a chronic incurable disease) = low incidence but high prevalence
because the prevalence is the cumulative sum of past year incidence rates
What are the main variables of descriptive studies
Time, place person
or
When, where, who
What are the advantages of using a sample of the population to survey
- reduces no. of individuals to be sampled
- reduces cost
- higher response rate
- higher quality of info collected
why must a sample of the population used for a study be representative of the population being investigated
to avoid bias
What are the different sampling techniques?
- simple random sample
- systematic sample
- stratified sample
- cluster sample
- multi-stage sampling
what is a simple random sample
e.g. use of table of random numbers
what is a systematic sample
individuals selected at regular intervals from population list
what is a stratified sample
ensures small sub-groups as sampling units e.g. school classes
what is multi-stage sampling
combines the other sampling techniques
What errors and bias can occur in survey methodology
- sampling bias/ selection bias
- response bias/ information bias
- measurement error
- observer variation (intra or inter) (intra = dentist x observation is the same, inter = dentist x and y is measuring in the same standard way)
- loss to follow up
