Epidemiology Flashcards
(38 cards)
What is standardization?
A set of techniques used to remove as far as possible the effects of differences in age or other cofounding variables when comparing ≥ 2 variables.
What are the methods of standardization?
- Direct method: A population distribution is the standard
- Indirect method: A set of specific rates is the standard
What is a standard population (direct standardization)?
Artificial populations with ficticious age structures, that are used in age standardization as uniform basis for the calculation of comparable measures for the respective reference populations.
When do we use indirect standardization?
- When age-specific rates are unavailable
- A set of rates from a standard population is applied to each of the populations being compared to calculate the standardized morbidity/mortality ratios (unlike direct standardization, where we take one population structure as standard and apply sets of rates to it to estimate expected events)
- Also used when comparing a small population
What are the advantages and disadvantages of standardization?
Advantages:
- Summarizes stratum-specific rates
- Unconfounded comparison of population
Disadvantages:
- Fictitious values
- Value depends on choice of standard
What are cross-sectional studies?
The presence or absence of disease (and other variables) are determined in each member of the study population or representative sample at a particular time.
- Disease prevalence can be assessed, not incidence
- At a same, given time on an individual level.
- They inform us on the frequency of the disease and the exposition factor at a given time (estimation of prevalence).
What are the main functions and planning of epidemiological studies?
Function:
- Collect, analyse and utilise health-related info to improve population health.
Planning:
- Proffessional (medical, epidemiological, ethical), administrative and economic considerations.
What are epidemiological studies?
- Mostly analytic or experimental
- Aim: detect cause-effect relationship between certain factors
What are the key components of epidemiological studies?
Types of epidemiological studies
What is a cohort study? List some of its characteristics!
Compare 2 groups, exposed Vs unexposed, which are followed over time to see the risk of a specific outcome. Outcome is disease incidence in each group.
- Exposure is measured prior to onset of disease
- Prospective, but may be historic (“restrospective”)
- Connection between an exposure and multiple outcome measures can be assessed simulatneously
- Incidence can be measured directly, but not prevalence
- Quite expensive, time consuming
- Large effort of organization and management (risk of discontinuation of participants)
What are Hill’s causal criteria?
- Strength of association (the stronger, the more palpable)
- Consistency (over space, time, method, research group, …)
- Dose-response relationship (larger dose ==> larger effect)
- Chronological relationship (cause before effect)
- Specificity (one-to-one relationship)
- Biological plausibility (is the relationship plausible at all?)
- Coherance (does it fit with specific established natural laws?)
- Analogy (with similar systems of causation)
- Experimental evidence
What are the 3 elements to measure disease incidence?
E (event - yes/no)
N (number of at-risk persons in the population under study)
T (time period during which events are observed)
What are the 2 types of prevalence?
Point prevalence: number of persons with a specific disease at one point in time divided by the total number of persons in the population.
Period prevalence: number of persons with disease in a time interval divided by the number of persons in the population (prevalence at the beginning of the interval + any incident cases).
For what do we use prevalence and incidence?
Incidence:
- Acutely acquired diseases
- About the etiology of the disorder
- Always requires a duration
Prevalence:
- More permanent states, conditions or attributes of ill-health
- About societal burden of the disorder including the costs and resources consumed as a result of the diosrder
- May or may not require duration
What are the 2 measures of incidence?
Cumulative incidence (incidence proportion) = CI:
- It is the proportion of individuals who experience the event in a defined time period (E/N during some time T)
- It has no dimension
- The value may vary between 0 and 1
- Specified in time (e.g. 5 years)
- All members of the given population should be observed until the occurrence of the event or until the end of the observational period
- Survival rate (SR): 1-CI
Incidence rate (density):
- It is the number of events divided by the amount of person-time observed (E/NT)
- Value may vary between 0 and infinity
- Number of new cases/(avg pop at risk x time interval) = number of new cases/population-time
- Rate at which new cases of a disease occur in a population given that the population is both studied and at risk for varying length of time
- Person-time = number of disease-free time contributed by each individual in the study
What types of prevention do we have?
Primary prevention:
- Promotes health at both individual and community levels by facilitating health-enhancing behaviors, preventing the onset of risk behaviors, and diminishing exposure to environmental hazards.
- It decreases disease incidence.
Secondary prevention (screening):
- Screens for risk factors and early detection of asymptomatic or mild disease, permitting timely and effective intervention and curative treatment.
- It decreases disease prevalence.
Tertiary prevention:
- Reduces the negative impact of established diseases by restoring function and reducing disease-related complications.
- It prevents recurrence and slow progression.
Quaternary prevention:
- Describes the set of health activities that mitigate or avoid the consequences of unecessary or excessive interventions in the health system.
What are the different kinds of testing in medicine?
Diagnostic: specifically looking for a suspected condition, which is tested for and confirmed or excluded.
Case-finding: in an investigation of exposed people, to sort the exposed + ill from the exposed + well
Opportunistic case-finding: Test is offered to a person without symptoms of the disease when they present to a health care practitioner for reasons unrelated to that disease.
Screening: No specific exposure or indication that the individual as a disease.
What types of screening do we have?
- Mass screening: no selection of population
- Selective screening (by age, sex)
- Multiphased screening (series of tests)
What are the principles of screening (WHO)?
- Condition has an important health problem
- Treatment should be available
- Facilities for diagnosis and treatment should be available
- Presence of a latent stage of the disease
- Possibility to test or examine the condition
- The test should be acceptable to the population
- Agreed policy on who to treat
- Costs fo finding a case should be balanced in relation to medical expenditure as as whole
- Case-finding should be a continuous process, not just a “once and for all” project
What are the characteristics of a good screening test?
- Valid
- Simple, quick
- Reliable
- Yield
- Cost-benifit
- Applicable and acceptable (discomfort, hassle, cost)
- Follow-up services (plan needed to deal with positive results
What is sensitivity?
- Tells us how well a positive test detects the agent to be screened. it is the percentage of true positives among patients indicated to be ill.
- Its counterpart is the false negative rate. Together, they add up to one.
What is specificity?
- Tells us how well a negative test detects non-disease. It is the percentage of true negatives among patients indicated to be well.
- Its counterpart is the false positive rate. Together, they add up to one.
How does changing the threshold for a test affect the sensitivity and the specificity?
- Lowering the threshold ==> improves sensitivity, but lower specificity.
- Raising the threshold ==> improves specificity, but lowers sensitivity.
