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Screening tests
Dr Mona Aboserea
professor of public health
SCREENING tests :
DEFINITION
Is the application of relatively simple and rapid test to a
large number of apparently health...
• Assessing a new diagnostic test is done versus an
accepted reference test known as “gold
standard”. By this gold standar...
-Disease/disorder should be
An important public health problem
High prevalence
Serious outcome
-Early Detection in a sy...
Screening Test
Concerned with a Functional Definition of
Normality versus Abnormality
Screening Test
Normal
Abnormal
Special requirements of Screening Tests
A-Valid: ability of the screening test to do
what is supposed to do. Measured by;
...
Special requirements of Screening Tests
b-Reliable: It is the ability of the test to give
same results when repeated under...
Group (a(
True Positive
Group (b(
False Positive
Group (c(
False Negative
Group (d(
True Negative
The 2x2 Table describes ...
Group (a(
True Positive
Group (b(
False Positive
Group (c(
False Negative
Group (d(
True Negative
Characteristics of Scree...
Group (a(
True Positive
Group (b(
False Positive
Group (c(
False Negative
Group (d(
True Negative
Characteristics of Scree...
200
True positive
0
False positive
0
False negative
800
True negative
Disease
present
Disease
absent
Positive
result
Negat...
170
True Positive
30
False Positive
30
False Negative
770
True Negative
Disease
present
Disease
absent
Positive
result
Neg...
3) Positive Predictive Value (PPV): The
likelihood that a positive test result indicates
the presence of the disease
(a)
(...
4) Negative Predictive Value (NPV): The
likelihood that a negative test result
indicates the absence of the disease
(d)
(c...
Criteria for Evaluating a Screening
Test
•Validity : provide a good indication of who does and does
not have disease
-Sens...
Validity of Screening Test (Accuracy)
- Sensitivity: Is the test detecting true cases of
disease? (Ideal is 100%: 100% of ...
• Advantages
• Disadvantages
Screening test
Gold standard test
test diseased healthy Total
positive a b a + b
negative c d...
Advantages:
Magnitude of disease can be precisely
assessed, where pre-symptomatic cases are
not missed.
Early detected c...
Disadvantages:
Not 100% accurate test. Detected cases may
be actually free of the disease (called false
positive), on the ...
1-Mass screening:
Large numbers of people are screened for
the presence of a disease without specific
reference to their i...
2-Selective screening: They are used to
detect specific disease in people who are
known to be at high risk.
e.g. screening...
3-Opportunistic screening: Applied when
the opportunity arises as for example in pre-
placement examination, examination o...
• Exercise .
A medical research team conduct a trial to
find if high plasma level of breast carcinoma
promoting factor (B...
Feedback of Exercise .8:- It is an example of studying
the performance of a new diagnostic test
PATHOLOGY
STUDIED
TEST
Br...
• Feedback of Exercise .8(cont.):-
• Sensitivity, specificity, predictive value positive &
predictive value negative can b...
Remember Steps in the
Research Process
1.Define the Problem
2. Review the literature
3-Conduct research on the problem.
4....
Steps in the Research Process
6. Conduct experiments, collect data.
7-Analyze the data
8. Present the results
9-Disseminat...
Screening  tests
Screening  tests
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Screening tests

  1. 1. Screening tests Dr Mona Aboserea professor of public health
  2. 2. SCREENING tests : DEFINITION Is the application of relatively simple and rapid test to a large number of apparently healthy people in order to classify them as likely or unlikely to have the disease. Screening: Considered a secondary preventive intervention
  3. 3. • Assessing a new diagnostic test is done versus an accepted reference test known as “gold standard”. By this gold standard individuals are labeled as either diseased or free. • Then, sensitivity, specificity, predictive value of positives & predictive value of negatives can be calculated for the new test. Researches to study the performance of a diagnostic test “ screening test’’
  4. 4. -Disease/disorder should be An important public health problem High prevalence Serious outcome -Early Detection in a symptomatic (pre-clinical) individuals is possible -Early detection and treatment can affect the course of disease (improve outcome) -Effective ttt is available for the detected disease. - Screening tests are simple, acceptable to population, inexpensive, noninvasive, not painful, and relatively accurate Criteria for Use of a Screening Test
  5. 5. Screening Test Concerned with a Functional Definition of Normality versus Abnormality Screening Test Normal Abnormal
  6. 6. Special requirements of Screening Tests A-Valid: ability of the screening test to do what is supposed to do. Measured by; –Sensitivity: ability to detect +ve cases among truly +ve –Specificity: ability to detect –ve cases among truly –ve – Positive Predictive Value: proportion testing positive who actually have the disease – Negative Predictive Value: proportion testing negative who do not have the disease
  7. 7. Special requirements of Screening Tests b-Reliable: It is the ability of the test to give same results when repeated under standard conditions.
  8. 8. Group (a( True Positive Group (b( False Positive Group (c( False Negative Group (d( True Negative The 2x2 Table describes screening test outcomes: Disease present Disease absent Positive result Negative result Application of Screening to Populations Diagnostic test or gold standardScreening test
  9. 9. Group (a( True Positive Group (b( False Positive Group (c( False Negative Group (d( True Negative Characteristics of Screening Tests 1) Sensitivity: proportion of those with disease who test positive in the screened group (a) (a) + (c) Positive result Negative result Disease present Disease absent Total
  10. 10. Group (a( True Positive Group (b( False Positive Group (c( False Negative Group (d( True Negative Characteristics of Screening Tests 2) Specificity: proportion of those without disease who test negative in screened group (d) (b) + (d) Positive result Negative result Disease present Disease absent Total
  11. 11. 200 True positive 0 False positive 0 False negative 800 True negative Disease present Disease absent Positive result Negative result n = 200 n = 800 The Ideal Situation--100% Agreement
  12. 12. 170 True Positive 30 False Positive 30 False Negative 770 True Negative Disease present Disease absent Positive result Negative result n = 200 n = 800 A More Likely Outcome
  13. 13. 3) Positive Predictive Value (PPV): The likelihood that a positive test result indicates the presence of the disease (a) (a) + (b) Characteristics of Screening Tests Group (a( True Positive Group (b( False Positive Group (c( False Negative Group (d( True Negative Positive result Negative result Disease present Disease absent Total
  14. 14. 4) Negative Predictive Value (NPV): The likelihood that a negative test result indicates the absence of the disease (d) (c) + (d) Characteristics of Screening Tests Group (a( True Positive Group (b( False Positive Group (c( False Negative Group (d( True Negative Positive result Negative result Disease present Disease absent Total
  15. 15. Criteria for Evaluating a Screening Test •Validity : provide a good indication of who does and does not have disease -Sensitivity of the test -Specificity of the test •Reliability=reproducibility=precision : gives consistent results when given to same person under the same conditions ‘’Agreement within and between examiners’’
  16. 16. Validity of Screening Test (Accuracy) - Sensitivity: Is the test detecting true cases of disease? (Ideal is 100%: 100% of cases are detected) -Specificity: Is the test excluding those without disease? (Ideal is 100%: 100% of non-cases are negative)
  17. 17. • Advantages • Disadvantages Screening test Gold standard test test diseased healthy Total positive a b a + b negative c d c + d Total a + c b + d a + b + c + d
  18. 18. Advantages: Magnitude of disease can be precisely assessed, where pre-symptomatic cases are not missed. Early detected cases can be effectively controlled, with better prognosis, no or minimal consequences and less burden on health services. Screening test
  19. 19. Disadvantages: Not 100% accurate test. Detected cases may be actually free of the disease (called false positive), on the other hand the test may diagnose actually diseased persons (false negative). The higher the percentages of false positive and false negatives the worse is screening test. Screening test
  20. 20. 1-Mass screening: Large numbers of people are screened for the presence of a disease without specific reference to their individual risk of having or developing the condition. As screening for type 2 DM in certain community. Types of Screening program
  21. 21. 2-Selective screening: They are used to detect specific disease in people who are known to be at high risk. e.g. screening for bone thickness among females at menopause, type 2 DM in obese persons, chest X-ray for males heavy smokers with chronic cough. Types of Screening program cont.
  22. 22. 3-Opportunistic screening: Applied when the opportunity arises as for example in pre- placement examination, examination of students at school entry and soldiers who join the army by general clinical examination, urine and stool analysis, blood picture, dental examination and visual acuity Types of Screening program cont.
  23. 23. • Exercise . A medical research team conduct a trial to find if high plasma level of breast carcinoma promoting factor (BCPF) could be used to diagnose breast cancer. • Out of 1600 patients included in the study, 600 demonstrated by breast biopsy (the gold standard) to have breast cancer (D+) and 1000 were found to be disease –free(D-) • Out of the 600 demonstrated to have breast cancer, 570 were positive by BCPF(T+) and Out of the 1000 were found to be disease – free, 850 were negative by BCPF(T-)
  24. 24. Feedback of Exercise .8:- It is an example of studying the performance of a new diagnostic test PATHOLOGY STUDIED TEST Breast cancer(D+) No breast cancer (D-) Total Marker (+) (T+) 570 (TP) 150 ( FP) 720 Marker (-) (T-) 30 (FN) 850 (TN) 880 Total 600 1000 1600
  25. 25. • Feedback of Exercise .8(cont.):- • Sensitivity, specificity, predictive value positive & predictive value negative can be calculated • Sensitivity= 570/600 = 0.95 = 95% • Specificity=850/1000 = 0.85 = 85% • Predictive value positive= 570/720 = 0.79=79.2% • Predictive value negative= 850/880 = 0.97=96.6%
  26. 26. Remember Steps in the Research Process 1.Define the Problem 2. Review the literature 3-Conduct research on the problem. 4. Define the population 5-clearly define terms & concepts
  27. 27. Steps in the Research Process 6. Conduct experiments, collect data. 7-Analyze the data 8. Present the results 9-Dissemination.
  • SUWILANJISilwizya

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    Dec. 4, 2020
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    Oct. 16, 2019

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