Epidemiology definition
The study of how much dis-ease occurs in a population and of factors that determine differences in dis-ease occurrence between populations at one point or over a period of time.
Dis-ease definition
Any health-related event or health-related state.
Goal of epidemiologists
Measure the frequency of health and disease in different populations. Find the causes of poor health and improve it.
Tend to study negative events/states
Look at quantitative data (categorical and numerical)
What does it mean if the frequency of dis-ease is different between 2 populations?
It can help identify the causes
The basic equation of epidemiology
Frequency = (# of cases of dis-ease) / (# in total population) / Time
Population/group definition
Any group of people who share a specified common factor
Occurrence definition
Non-dis-eased to dis-eased state
How does an epidemiological study always start? Then what happens?
By first describing the population (denominator) then counting the number of cases if dis-ease that occurs in the population (numerator)
Describe PECOT
Participants Exposure group Comparison group Outcome Time
Cohort study
Follows members of group overtime and counts relevant dis-ease events.
Also called follow up study
Measures incidence
Cross-sectional study
Measures population, exposure and disease prevalence at the same time
Often found via survey
Incidence
- Downward arrow
- Calculated by counting the number of disease event over a period of time
- Used for diseases with an easily observable occurrence point
- Presented as a proportion or percentage and accompanied by stating a time period
Prevalence
- Calculated by counting the number of people with a disease at a point in time
- Time is not included in the calculation
- Used for diseases with no observable onset point so it measures if dis-ease has occurred
- Prevalence measures can be categorical or numerical
Point prevalence
Where dis-ease state can easily be observed at one point in time. Horizontal arrow
Period prevalence
- Where disease cannot easily be measured at one point so must be measured by the number of people who experienced it in the past.
- Often measured via survey
- Sloped arrow
Prevalence with categorical numerator
Will be a proportion/percentage
Prevalence with numerical numerator
WIll be a mean/average
What is prevalence affected by
- The cure rate
- The death rate
- Rate of disease occurrence (incidence)
- Population with high incidence could have low prevalence if death/cure rate was high
- Population with low incidence could have high prevalence if death/cure rate was low
Ecological study
Compares whole groups of populations rather than individuals
RCT
- Like a cohort study
- Participants are allocated to exposure and comparison groups randomly
- Intervention is involved
- EG and CG at same baseline
Single blind
Participants don’t know wht intervention they have EG or CG
Double blind
Neither participants nor investigators
