Module 1 (+ Module 3-1) Flashcards
Epidemiology
Study of frequency/occurrence of dis-ease in populations
- differences/similarities in frequency between populations helps identify causes
Process of epidemiology
1) describe a population
2) count total population
3) count number of cases of dis-ease
Formula:
E = N/D/T
Need for age standardisation/adjustment
Can only compare ‘like with like’ (confounding)
Numerical values
- convert into categorical measures
- use mean or median level of outcome
Cohort study
Allocation into EG and CG: measured exposures
Measurement of outcome: followed over a period of time
Cross-sectional study
Allocation into EG and CG: measured exposures
Measurement of outcomes: at the same time as measurement of exposures
Incidence
- Outcome events counted forward from starting point, over a period of time
- time included in calculation
- rate
- preferred method if easy to observe events
- depends ONLY on no. Events during specified time period
Incidence type of study and data
ONLY cohort, ONLY categorical
Prevalence
- no. People with disease counted at ONE POINT in time
- time not included in calculation but when counted is mentioned
- state
- depends on incidence, deaths and cures
Prevalence types of study and data
Both cross-sectional and cohort (one point during the study)
Categorical and numerical
Change in prevalence
Difference between prevalence measured at two points in time
Retrospective info
If events come and go frequently
1) use incidence over a retrospective time period to group people into categories
2) total number of episodes for each group is outcome (no. Episodes for each individual person is not used in calculation)
Measures prevalence because deaths/cures are lost
Cohort/cross-sectional study depending on when exposures are measured in relation to outcomes
If most people died rapidly or were cured
High incidence disease has low prevalence
If few people died or were cured
Low incidence disease has high prevalence
Incidence strengths
- determined only by disease risk - clean measure
- includes N, D AND time - more info
Incidence weaknesses
- can be difficult to measure
- must be observed over time
Prevalence strengths
Relatively easy to measure
Prevalence weaknesses
- determined by incidence, cure rate and death rate - dirty measure
- doesn’t include time - less info
Ecological studies
Populations allocated to EG and CG (exposures are an average of a group of people)
Individual participant studies
Individuals are allocated to EG and CG
Reasons against RCT
Unethical, impractical
Blinding
Double-blind: neither participants nor investigators know which intervention was given to which participant
Single-blind: participants don’t know which intervention was given to which participant but investigators do
Only really works for experimental studies
Estimates of effect
Comparisons of disease occurrence in EG and CG
- gives idea of size of effect of study exposure on disease outcome
RR description
The risk of x in A is n times higher/lower than in B
- use RRI if higher, RRR if lower