Epidemiology Flashcards
What is epidemiology ?
The study of the distribution and determinants of health-related states or events in specified populations, neighbourhoods, school, city, county, state, country, globe and the application of this study to control of health problems.
Factors that influence disease epidemiology
Disease type
Mode of transmission
Genetic composition
Environment
Behaviour
Pathogenic virulence
Vaccination status
Disease type
Communicable - infectious (widespread)
Non-communicable - (localised)
Mortality rate
Mortality rate is an estimate of the portion of a population that dies during a specified time period.
Statistics needed for mortality rate
A denominator population
A time frame
Case fatality rate
The proportion of cases of a specified condition that are fatal within a specified time.
Weaknesses of CFR estimation
May underestimate (esp in early days) of outbreak / if there are breakdowns in reporting system
May overestimate if the denominator is limited
It assumes all cases have been tested
Infection fatality rate
The proportion of cases of a specified condition that die divided by the total infected people.
- depends on detection and reporting of asymptomatic or mild cases
Infection rate
The rate at which the infection spreads within a population
Ro < 1 : spread is less likely
Ro > 1 : spread is more likely
Larger the Ro : the harder it is to control the spread of disease
Denominators
Health board
City
Hospital
Disease register
Recruited to a study
Mortality rate
No people died / population x 100
Person time
The time period (e.g. number of years) that a person is exposed to risk.
N year follow up
The time period for which a cohort of people have been followed up for a given condition.
Incidence
Number of new cases
Number of new people with outcome over a time / total number of people in the group at risk
Multiplied by the population
Prevalence
Proportion of population that has disease at a given time.
Point : at a specified time
Period : over a specified period
Incidence vs Prevalence
Incidence : useful for identifying causes of disease
prevalence : identifies disease burden
Patterns of outcome occurrence
Sporadic
Endemic
Outbreak
Epidemic
Pandemic
Outcomes
Death
Hospitalisation
Quality of life
Surrogates
Exposure
Non-modifiable : age, sex, genotype
Modifiable : smoking, weight, diet
Interventions : drug therapy, surgery
Risk equation
Number of outcomes in a group / number of people in a group x100
Relative risk equation
Risk in exposed / risk in unexposed
Relative risk reduction
(1- relative risk) x 100
Absolute risk reduction
Risk in unexposed - Risk in exposed
Number needed to treat
1 / Absolute risk reduction
Confidence intervals
A range of plausible values
Wider interval : greater the uncertainty
Hierarchy of evidence
From bottom to top : less prone to confounding and bias
Top : more likely to influence clinical practice
Cross-sectional study
(include objective and time frame of study)
Sample a population
Estimate the proportion
Use data
PREVELENCE
PAST
Case control study
(include objective and time frame of study)
Select cases with an outcome
Select controls without the outcome
Explore exposures in cases and controls
Compare exposures in cases and controls
Identify association
CAUSE
PAST
Cohort study
(include objective and time frame of study)
Select people without an outcome
Classify according to exposure
Follow up
Compare risk of disease in exposed and unexposed
CAUSE, PROGNOSIS, INCIDENCE
FUTURE, PAST
Randomised control trial
(include objective and time frame of study)
Random allocation
Compare risk of outcome in intervention and control groups.
TREATMENT EFFECT
PAST
Systematic error
What/How data is collected
How data is analysed/interpreted/reported
