Chapter 11: Screening for Disease Flashcards
What is mass screening?
Also called pop. screening. Refers to the screening of total pop.groups on a large scale
What is selective screening?
Also called targeted screening. Applied to subsets of the pop. at a high risk for disease or certain conditions as the result of family history, age, or previous exposures.
What is screening?
examination of a group of usually asymptomatic individuals to detect those a high probability of having or developing a disease
-Secondary prevention
Uses of screening?
- detect cases (to test in patients for cancer, etc.)
- control of disease
- research
- education
What makes a good screening?
- Simple: easy to learn
- Rapid: quick to administer and get results
- Inexpensive: good cost ratio benefit
- Safe: no harm to participants
- Acceptable to target group
Validity?
Accuracy
-the ability of a test to predict if a person has the disease or not; a true measure
Valeria was accurate about the test she performed on herself. She had Leukemia
Reliability?
Precision. Consistency
-the ability of a test to give consistent results when performed more than once on the same person under the same conditions
Types of validity?
- Content
- Criterion referenced
- Construct
Measurement error?
constant errors introduced by a faculty measuring device and tend to reduce the reliability of measurements
Halo Effect?
the influence upon an observation of the observer’s perception of the characteristics of the individual observed
Social desirability effect?
Someone answers in a way that is agreeable w/ other people
Sensitivity?
the ability of a test to correctly identify those w/ the disease or condition (true positives)
-high sensitivity
Is there a difference between screening and diagnosis?
Yes. Screening tests evaluate an individual’s risk of developing a genetic condition, while diagnostic tests identify genetic conditions.
- Positive screening results are followed by diagnostic tests to confirm actual disease
- Screening is more of testing on an individual to see if there is a disease inside of them.
Types of screening?
- Mass screening
- Selective screening
- Multiphasic screening
Mass screening?
Screening on a large scale of total population groups, regardless of risk status, usually for research or surveillance purposes
Selective screening?
Screening of selected groups of people in high risk categories
Multiphasic screening?
Multiple screening tests together among a large group of people
What are societal considerations of screening?
- Condition should be important to the individual and the community
- Favorable cost ratio benefit
- High public acceptance of the test
Scientific considerations?
- Natural history of the condition should be understood properly
- A knowledge base is good for prevention and occurrence of disease
Ethical considerations?
- The program can alter the natural history of the condition in a significant proportion of those screened
- Suitable, acceptable tests for screening and diagnosis of the condition are available
- Acceptable, effective methods of prevention are available
Types of reliability?
- Repeated measurement
- Internal consistency
- Interjudge
What is repeated measurement reliability?
the degree of consistency among repeated measurements of the same individual on more than 1 occasion
What is internal consistency reliability?
evaluates the degree of agreement or homogeneity
within a questionnaire measure of an attitude, a personal characteristic, or a psychologic attribute
What is interjudge reliability?
reliability assessments derived from agreement among trained experts
What is content validity?
The degree to which the measurement incorporates the domain of the phenomenon under study
What is criterion-referenced validity?
Found by correlating a measure with an external criterion of the entity being assessed
What is construct validity?
Degree to which the measurement agrees with the theoretical concept being investigated
Are validity and reliability direct or inverse?
Inversely proportional
-when one goes up, the other is down
Sensitivity?
The ability of a test to correctly identify those with the disease or condition (true positives)
-Formula: a/a+c
Specificity?
The ability of a test to correctly identify those without the disease or condition (true negatives)
-Formula: d/b+d
What is PPV?
Positive Predictive Value; PV+. The probability of having the disease if you test positive.
- The proportion of people who screen + and truly have the disease
- a/(a+b)
What is NPV?
Negative Predictive Value; PV-. The probability of not having the disease if you test negative.
- The proportion of people who screen - and truly do not have the disease
- d/(c+d)
Prevalence=?
those who were screened who have the disease
-(a+c)/(a+b+c+d)
Accuracy? (efficiency)
- those who were screened who received correct test results
- (a+d)/(a+b+c+d)
If you have a fatal disease with no treatment (such as
Creutzfeldt-Jakob disease), optimize what? Why?
Specificity; b/c
If you are screening to prevent transmission of a preventable disease (such as screening blood donors), optimize what? Why?
Sensitivity;
Lead time bias?
The perception that the screen-detected case has longer survival because the disease was identified early
Length bias?
Tumors identified by screening are slower growing and have a better prognosis.
Selection bas?
Motivated participants have a different probability of disease than do those who refuse to
participate.
