[SAR HS 300] - Midterm Exam Guide - Everything you need to know! (43 pages long)

114 views43 pages

For unlimited access to Study Guides, a Grade+ subscription is required.

BU
SAR HS 300
MIDTERM EXAM
STUDY GUIDE
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 43 pages and 3 million more documents.

Already have an account? Log in
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 43 pages and 3 million more documents.

Already have an account? Log in
Measure of Validity of Screening Tests
1.!Sensitivity: the extent to which a test identifies as
positive all individuals who have a given disease.
a/(a+c)
2.!Specificity: the extent to which a test identifies as
negative all individuals who are free of a given
disease. d/(b+d)
Example: 500 elderly individuals are screened for diabetes
with a fasting blood glucose. 265 screened positive. The 265
positive screened then underwent a glucose tolerance test
(GTT) and 240 were positive. The 235 who screened negative
underwent GTT and 15 tested positive. Calc sensitivity and
specificity of screening test
!Prevalence: 255/500
!Sensitivity (a/a+c) = 240/255 x 100 = 94.1.
Interpretation: Among those tested, 94.1% of persons with diabetes screened positive by fasting
blood glucose screening test.
SO 5.9% WERE FALSE NEGATIVES
!Specificity (d/b+d) = 220 / 245 x 100 = 89.8. Interpretation: Among those tested, 89.8% of those
without diabetes screen negative by fasting blood glucose screening test.
SO 10% WERE
FALSE POSITIVES
Normal Range: decided as 2 standard deviations from the mean
Relationship between sensitivity and specificity
A successful screening test will balance cut point criteria so that both over-referrals and under-referrals
for diagnostic tests are minimized.
Measure of Accuracy of Screening Tests
Accuracy: of a screening test is the degree of agreement between the screening test and the gold standard,
and is calculated by: (a+d)/(a+b+c+d)
Predictive Value:
!Positive Predictive Value: the proportion of individuals screened positive by the test who actually
have the disease. a/(a+b)
among this screened population, _ % of those who screened positive for diabetes by fasting
blood glucose screening test truly have diabetes.
!Negative Predictive Value: the proportion of individuals screened negative who are actually free
of the disease. d/(c+d).
Among this screened population, 93.6% of those who screened negative for diabetes by fasting
blood glucose are truly free of the disease
SUMMARY
find more resources at oneclass.com
find more resources at oneclass.com
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 43 pages and 3 million more documents.

Already have an account? Log in
Prevalence: effects of prevalence of disease on screening test results
!Positive and negative predictive value are affected by prevalence of disease.
!When the prevalence of a disease falls, the positive predictive value falls, and the negative
predictive value rises.
If prevalence RISES:
!Number of false negatives DECREASES
!Positive predictive value INCREASE
!Would NOT CHANGE that sensitivity and specificity
Screening program feasibility: Once acceptable sensitivity and specificity levels of screening test are
attained
!The predictive value is the main way to measure a screening program’s feasibility
Characteristics of Diseases Appropriate for Screening
1)!Serious disease with serious consequences
2)!Treatment more effective at earlier stages
3)!Has a detectable preclinical phase
4)!Preclinical phase is long (> year)
Characteristics of a good screening test
!Simple
!Rapid
!Inexpensive
!Safe
!Acceptable
!Valid
Example of good screening tests: Serology - HIV and Hepatitis B
!Mammogram breast cancer
!Pap smear cervical cancer
!BP & cholesterol heart disease
!Stool guaiac colorectal cancer
!Eye examsglaucoma
!(Prostate cancer blood PSA (now under
debate)
find more resources at oneclass.com
find more resources at oneclass.com
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 43 pages and 3 million more documents.

Already have an account? Log in

Get access

Grade+
$10 USD/m
Billed $120 USD annually
Homework Help
Class Notes
Textbook Notes
40 Verified Answers
Study Guides
1 Booster Class