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)
