screening only] [compatibility mode]
TRANSCRIPT
-
8/3/2019 Screening Only] [Compatibility Mode]
1/21
Screening
-
8/3/2019 Screening Only] [Compatibility Mode]
2/21
Definition
The presumptive identification of unrecognized disease
or defect by the application of tests, examination or
other procedures which can be applied rapidly.
Screen ng sort out apparent y we persons w o
probably have a disease from those probably do not.
-
8/3/2019 Screening Only] [Compatibility Mode]
3/21
Main Aim of Screening
To reverse, halt, or slow the progression of disease
more effectively than would probably normally happen.
To alter the natural course of disease for a better
outcome or n v ua s a ecte .
Reduce morbidity and mortality through early detection and treatment
-
8/3/2019 Screening Only] [Compatibility Mode]
4/21
h r Aim f r nin
Protect society from contagious disease
Rational allocation of resources
e ec on o ea y n v ua s:
employment, military
Research; study on natural history of
-
8/3/2019 Screening Only] [Compatibility Mode]
5/21
Two-by-Two Table for Screening Evaluation
Measures of validity: sensitivity and specificity
-
8/3/2019 Screening Only] [Compatibility Mode]
6/21
Sensitivity of a Screening Test
Sensitivity : the proportion of people with a disease
who have a positive test for the disease
a/a+c
-
8/3/2019 Screening Only] [Compatibility Mode]
7/21
Specificity of a Screening Test
Specificity is the proportion of people without the
disease who have a negative test
d/b+d
-
8/3/2019 Screening Only] [Compatibility Mode]
8/21
Positive Predictive Value
Positive predictive value: is the probability of the
presence of the disease in a person with a positive(abnormal) test result.
(+PV = a/a+b)
-
8/3/2019 Screening Only] [Compatibility Mode]
9/21
Negative Predictive Value
Negative predictive value is the probability of not
having the disease when the test result is negative(normal).
(-PV = d/c+d)
-
8/3/2019 Screening Only] [Compatibility Mode]
10/21
-Disease serious & High risk with further
Disease is highly
communicable
agnost c tec n ques
High cost with further
Subsequent evaluation of
positives is not costly and
No definitive treatment
exist
has minimal risk
Sensitivity Specificity
Sensitivity and specificity are affected by the cut-off value of measure at
which a test is defined as positive.
-
8/3/2019 Screening Only] [Compatibility Mode]
11/21
Predictive Value Positive (Yield)
The yield of a test result is affected by:
Specificity of the test
Prevalence of the disease
-
8/3/2019 Screening Only] [Compatibility Mode]
12/21
,specificity and prevalence on yield
-
8/3/2019 Screening Only] [Compatibility Mode]
13/21
Changing Sensitivity
-
8/3/2019 Screening Only] [Compatibility Mode]
14/21
Changing Specificity
-
8/3/2019 Screening Only] [Compatibility Mode]
15/21
Changing Prevalence
-
8/3/2019 Screening Only] [Compatibility Mode]
16/21
Strategies to Increase Yield
Select a test with high specificity Hi h sensitivit > Low false - > Hi h PV-
High specificity > Low false + > High PV+
Select disease with hi h revalence of re-clinical stage
-
8/3/2019 Screening Only] [Compatibility Mode]
17/21
Success Factors for Screening Programs
The health problem should be important enough to be worth detecting.
Availability of an acceptable intervention which is effective.
Presence of a recognizable latent or early "asymptomatic" stage.
Presence of a suitable and acceptable test.
The natural history of the condition should be adequately understood.
Presence of policy regarding when the intervention is appropriate.
The cost of detecting the problem and its remedy should be reasonable.
" ", - .
-
8/3/2019 Screening Only] [Compatibility Mode]
18/21
Potential Source of Bias in Screening
Self-selection (volunteer) bias
Lea t me as ear y agnos s
-
8/3/2019 Screening Only] [Compatibility Mode]
19/21
-
-
8/3/2019 Screening Only] [Compatibility Mode]
20/21
Length Bias in Screening
-
8/3/2019 Screening Only] [Compatibility Mode]
21/21
Study Design for Evaluation of Screening
Ideally experimental
Most commonly used is cohort