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Pubic health I > Epidemiology > Flashcards

Epidemiology Flashcards

1
Q

What is standardization?

A

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.

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2
Q

What are the methods of standardization?

A
  • Direct method: A population distribution is the standard
  • Indirect method: A set of specific rates is the standard
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3
Q

What is a standard population (direct standardization)?

A

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.

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4
Q

When do we use indirect standardization?

A
  • 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
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5
Q

What are the advantages and disadvantages of standardization?

A

Advantages:

  • Summarizes stratum-specific rates
  • Unconfounded comparison of population

Disadvantages:

  • Fictitious values
  • Value depends on choice of standard
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6
Q

What are cross-sectional studies?

A

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).
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7
Q

What are the main functions and planning of epidemiological studies?

A

Function:

  • Collect, analyse and utilise health-related info to improve population health.

Planning:

  • Proffessional (medical, epidemiological, ethical), administrative and economic considerations.
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8
Q

What are epidemiological studies?

A
  • Mostly analytic or experimental
  • Aim: detect cause-effect relationship between certain factors
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9
Q

What are the key components of epidemiological studies?

A
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10
Q

Types of epidemiological studies

A
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11
Q

What is a cohort study? List some of its characteristics!

A

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)
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12
Q

What are Hill’s causal criteria?

A
  • 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
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13
Q

What are the 3 elements to measure disease incidence?

A

E (event - yes/no)

N (number of at-risk persons in the population under study)

T (time period during which events are observed)

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14
Q

What are the 2 types of prevalence?

A

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).

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15
Q

For what do we use prevalence and incidence?

A

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
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16
Q

What are the 2 measures of incidence?

A

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
17
Q

What types of prevention do we have?

A

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.
18
Q

What are the different kinds of testing in medicine?

A

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.

19
Q

What types of screening do we have?

A
  • Mass screening: no selection of population
  • Selective screening (by age, sex)
  • Multiphased screening (series of tests)
20
Q

What are the principles of screening (WHO)?

A
  • 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
21
Q

What are the characteristics of a good screening test?

A
  • Valid
  • Simple, quick
  • Reliable
  • Yield
  • Cost-benifit
  • Applicable and acceptable (discomfort, hassle, cost)
  • Follow-up services (plan needed to deal with positive results
22
Q

What is sensitivity?

A
  • 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.
23
Q

What is specificity?

A
  • 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.
24
Q

How does changing the threshold for a test affect the sensitivity and the specificity?

A
  • Lowering the threshold ==> improves sensitivity, but lower specificity.
  • Raising the threshold ==> improves specificity, but lowers sensitivity.
25
Q

What is the positive predictive value?

A

It is the percentage of true positive among patients indicated to be positive

26
Q

What is the negative predictive value?

A

It is the percentage of true negatives among patients indicated to be negative.

27
Q

What are the disadvantages of screening?

A
  • Cost and use of medical resources on a majority of people who don’t need treatment
  • Adverse effects of screening procedures
  • Stress and anxiety caused by false positive
  • Unnecessary investigation and treatment of false positive
  • Stress and anxiety due to prolonged knowledge of an illness without any improvement in outcome
  • A false sense of security caused by false negative
28
Q

What are the different states of diseases and their progression?

A
  • S0: disease-free state (ø disease, and can’t be detected by test)
  • Sp: preclinical state (Disease, but no signs or symptoms. Can be detected by test)
  • Sc: clinical state (diagnosis by usual care)

Non-progressive model:

S0 <-> Sp -> Sc

Progressive disease model:

S0 –> Sp –> Sc

OR

29
Q

What is a case-control study? Give examples of their use?

A
  • It is an observational study used to identify risk factors for a disease/outcome.
  • It is a retrospective type of study
  • A group of people with the disease is identified and compared with a suitable comparison group without the disease
  • Can’t assess incidence, but rather prevalence

Examples of uses:

  • Outbreak investigation
  • Birth defects (exposures)
  • New disease (DES and vaginal cancer in adolescents or smoking with lung cancer)
30
Q

What are the pros and cons of case-control studies?

A

Pros:

  • Cases easily available
  • Good for less common or rare cases
  • Quick, inexpensive
  • Can be conducted by clinicians in clinical facilities
  • Support, but usually doesn’t prove causal hypothesis by establishing associations
  • Historical data available in clinical records
  • Number of subjects needed is small

Cons:

  • Patient history is biased as it depends on memory
  • Clinical data may be incomplete
  • Case group may not be homogenous
  • Berkson’s fallacy: generalizing from hospital or clinical samples to the general population
  • Can’t know the association for all or for a representative sample of all people having antecedent
31
Q

What are experimental/intervention studies?

A
  • Administration of an intervention, drug and observation of the outcome
  • Tightly controlled lab experiment to large scale community intervention
  • Randomization is essential for avoiding biased results.
  • Focus on how to measure the effect of an exposure on the outcome with consideration of potential confounders, efficacy of delivery of the intervention, …
32
Q

What are the types of intervention studies?

A

Prophylactic Vs Treatment:

  • Evaluate efficacy of intervention designed to prevent disease
  • Evaluate efficacy of curative drug or intervention (or drug to manage symptoms)

RCT Vs community trials:

  • Individuals, thighly controlled, narrowly focused, highly selected groups, short or long duration
  • Cities/regions, less rigidly controlled, long duration, usually primary prevention
33
Q

What are community trials for in intervention studies?

A
  • Whole population is studied
  • Focused on mass education campaigns ==> change peoples knowledge and attitude
  • Mainly about nutrition, health, economics
34
Q

What are individual trials used for?

A

Subdivided as:

  • Clinical trials: therapeutic, 2nd, 3rd prevention
  • Field trials: primary prevention
  • Intervention studies: individuals with outcome of interest above a certain level are excluded
35
Q

Why is randomization so important in intervention studies?

A
  • Assurance that control group is a valid substitute population
  • Only way to control unknown factors
  • Masks exposure status
  • Avoids ambiguity of time order of exposure and outcome
  • Foundation for statistical test
36
Q

What methods are used for randomization in intervention studies?

A
  • Coin toss
  • Random number tables, computer program
  • Done by a 3rd party
  • If physician is not blinded, assignment done by central call-in center or put in opaque envelopes and revealed to investigator at last possible time
37
Q

What special forms of randomized clinical trials are there?

A

Cross-over studies:

The palcebo and the active drug are switched half-way. Patients serve as their own control

Factorial design:

The same population tests 2 different drugs simultaneously. We assume the outcomes for each drug is different and that their modes of action are independent.

38
Q

What are the pros and cons of RCT?

A

Pros:

  • Highly internal validity
  • Able to control selection, confounding and mesurement biases
  • True measure of treatment efficacy

Cons:

  • Generalizability
  • Strict enrollement criteria creates a highly selected population
  • Complicated, expensive, time consuming
  • Ethical and practical limitations

Pubic health I (4 decks)

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