Chapters 15 & 16 Flashcards
How is screening defined?
The presumptive identification of an unrecognized disease or defect by the application of tests, examinations, or other procedures which can be applied rapidly.
What is the purpose of primary prevention?
prevents disease from occurring; goal is to reduce incidence
What is the purpose of secondary prevention?
Delays onset and duration of clinical disease. Goal is to improve survival.
What is the purpose of tertiary prevention?
Slows disease progression; reduces disease sequelae; goal is to improve survival
What are the characteristics of diseases appropriate for screening?
Disease is serious with severe consequences
Treatment is more effective at an earlier stage
Disease has a detectable preclinical phase
DPCP is fairly long and prevalent in the target population
What are the main characteristics of a screening test?
Validity
Reliability
Source of Test Errors
Criterion of Positivity
Sensitivity
Specificity
What is reliability?
the ability of a test to give the same result on repeated testing
What is validity?
the ability of a test to correctly identify individuals who do and do not have preclinical disease
What is sensitivity?
the probability that a test correctly classifies positive individuals who have the preclinical disease
What is specificity?
the probability that a test correctly classifies individuals without preclinical disease as negative
What is lead time?
The amount of time that the disease diagnosis is advanced by screening.
What is a screening program?
A set of procedures for early detection and treatment of a disease that is available to a population
What is a predictive value?
the main way to measure a screening program’s feasibility.
Two components:
Predictive Value Positive (PVP) - proportion of individuals with a positive test who have the preclinical disease -
Predictive Value Negative (PVN) - the proportion of individuals without the preclinical disease who test negative
What is lead time bias?
Lead time bias refers to a distortion overestimating the apparent time surviving with a disease caused by bringing forward the time of its diagnosis.
What is length bias sampling?
Length time bias is an overestimation of survival duration due to the relative excess of cases detected that are asymptomatically slowly progressing, while fast progressing cases are detected after giving symptoms.
What is volunteer bias?
The decision to be screened is influenced by a person’s health awareness, which may be related to his / her subsequent morbidity and mortality
What are typical outcomes used to measure the success of a screening program?
process measures
survival
shift in stage distribution
overall mortality
cause specific mortality
What is the usual effect of developing a widespread screening program?
The incidence rate of the target disease increases at first and then declines as a result of the earlier diagnosis of cases
What was the result of implementing breast cancer screening through the 1990s?
Reduced the risk of dying by about 30% among women ages 50 to 69 after 10-12 years of follow up.
Describe the prevention timeline
Describe the effects of screening on prostate cancer
How do epidemiologists Rothman, Greenland, and Lash define a “cause”?
an event, condition, or characteristic that preceded the disease onset and that, had the event / condition / characteristic been different… the disease would not have occurred at all or would not have occurred until some later time.”
When is an association considered valid?
When 3 other alternative explanations (bias, confounding, random error) have been eliminated / disproven
What are the attributes of a cause according to Susser?
Association, time order (cause leads to effect), and direction (x leads to y but not vice versa)
What are other attributes of causes?
They may include host / environmental factors
They may be passive or active
They may be either positive or negative associations
Who introduced the idea of the 4 humours?
Hippocrates (circa 400 BC)
Suggested that imbalances in these were caused by changes in seasons, elements, nature, and personal habits
Who introduced Germ Theory?
Louis Pasteur, Miles Berkeley, and many others in the mid 1800s
What did people believe caused illness prior to germ theory?
(prior to the 1800s) sin
(early 1800s) spontaneous generation or foul clouds (miasmas)
What were Henle and Koch’s postulates (mid to late 1800s)?
- The agent must be demonstrable in every case of the disease; 2. The agent is not present in other diseases; 3. After isolation in culture, the agent must be able to produce the disease in experimental animals; and (added by Koch) 4. The agent can be recovered from the experimental animal.
What are limitations of Henle / Koch’s Postulates?
They apply well to infectious disease but not to non-communicable diseases (particularly postulate 1)
When were the modern “causal criteria” first introduced?
In the 1950s and 1960s; 5 were presented in the 1964 Report of the Advisory Committee to the Surgeon General on Smoking and Health (to prove smoking causes lung cancer)
What is the best known criteria for assessing causation?
1965 - Sir Austin Bradford Hill’s 9 criteria / guidelines
What are Hill’s causation critera?
- strength of association
- consistency
- specificity
- temporality
- biological gradient
- plausibility
- coherence
- experiment
- analogy
Should we wait until proving causation to recommend public health strategies?
No - we have a moral obligation to suggest sooner
How does Rothman define “sufficient cause?”
a complete causal mechanism that inevitably produces disease
(not a single factor but a minimal set of factors - this may include the presence of causative exposures and lack of preventative exposures)
What is a component cause?
Each single factor in a sufficient cause
What is an example of Rothman’s 1970 sufficient component theory?
a person cannot get AIDs unless he/she is susceptible AND is exposed to HIV AND has unprotected intercourse (etc.)
What are important factors of sufficient component theory?
1 disease may have several different “cause constellations”
blocking the action of a single cause component stops the completion of the sufficient cause and thereby prevents disease from occurring by that pathway
completion of a sufficient cause is synonymous with biological disease onset
component causes may act far apart in time
Describe Rothman’s Causal Pies
Describe the web of causation for Lead Poisoning
Describe different types of Dose Response relationships
