quality assurance and control. objectives to define and discuss quality control to discuss the key...
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Quality Assurance and Control
Objectives
• To define and discuss quality control
• To discuss the key features of the design of epidemiologic studies
• To discuss data control instruments
• To discuss training of staff issues
QualityAssurance
• Steps in Quality Assurance– Specify study hypothesis– Specify general design to test study hypothesis
(study protocol)– Choose and prepare specific instruments (develop
operation manuals)– Train staff (certify staff)– Using trained staff, pretest and pilot-study data
collection– If necessary, modify 2 and 3
Key features of study design (1989 Kahn and Sempos)
• Formulation of the main hypothesis• A priori specification of potential confounding variables• Definitions of the characteristics of the study population• Definition of the design strategy for internal validity• Definitions of the design strategy for reliability and validity• Specifications of the study power• Standardization of procedures• Activities during data collection• Data analysis• Reporting of data
Some quantitative measures of validity and reliability
• Validity– Sensitivity– Specificity– Predictive value positive– Predictive value negative
• Reliability– Youden’s J statistic– Kappa scores
Example of temporal drift in measurement
Phantom measurements
Influence of Prevalence on Predictive Values
0
20
40
60
80
100
120
1 2 3 4 5 6
Prevalence
Pre
dic
tive
Va
lue
(%
)
PPV NPV
Predictive Values at Different Prevalence Rates with Sensitivty .90 and Specificity .90
G.S. + G.S. -N.T. + 9 9N.T. - 1 81
Total 10 90
G.S. + G.S. -N.T. + 22 7N.T. - 3 68
Total 25 75
G.S. + G.S. -N.T. + 45 5N.T. - 5 45
Total 50 50
Prev 10%PPV .50NPV .99
Prev 25%PPV .76NPV .96
Prev 50%PPV .90NPV .90
Spectrum of severity
Predictive Values
Culture + Culture -
PCR+ 80 10
PCR - 20 90
100 100
Kappa Statistic
• po = observed probability of concordance between the two surveys
• pe = expected probability of concordance between the two surveys
• The standard error of the Kappa statistic is calculated by:
• To test the hypothesis Ho:=0 vs. H1:0, use the test statistic:
Percent agreement
Figure 1. Association of average faculty performance rating (from 1, bottom 20%, to 5, top 20%) and absolute rank on the National Resident Matching Program (NRMP) list (r = 0.19; P =.11).
Table 1. Discrepancy Between the DIS and SCAN for the Lifetime Occurrence of Depressive Disorder in the
Baltimore ECA Follow-up*
Table 1-Comparison of WHO and ADA diagnostic categories for undiagnosed diabetes From: Lee: Diabetes Care, Volume 23(2).February 2000.181-186