HED 343 Chapter11 - Chapter 11 Chapter 11 Screening for...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Chapter 11 Chapter 11 Screening for Disease in the Community Screening for Disease Screening for Disease Screening­­the presumptive identification of unrecognized disease or defects by the application of tests, examinations, or other procedures that can be applied rapidly. Positive screening results are followed by diagnostic tests to confirm actual disease. Multiphasic Screening Multiphasic Screening Defined as the use of two or more screening tests together among large groups of people. Information obtained on risk factor status, history of illness, and health measurements. Commonly used by employers and health maintenance organizations. Mass Screening and Selective Screening Mass Screening and Selective Screening Mass screening­­screening on a large scale of total population groups regardless of risk status. Selective screening­­screens subsets of the population at high risk for disease. More economical, and likely to yield more true cases. Example: Screening high­risk persons for Tay­Sachs disease. Mass Health Examinations Mass Health Examinations Population or epidemiologic surveys­­purpose is to gain knowledge regarding the distribution and determinants of diseases in selected populations. No benefit to the participant is implied. Mass Health Examinations (cont’d) Mass Health Examinations Epidemiologic surveillance­­aims at the protection of community health through case detection and intervention. Case finding ­­the utilization of screening tests for detection of conditions unrelated to the patient’s chief complaint. Appropriate Situations for Appropriate Situations for Screening Tests and Programs Social Scientific Ethical Social Social The health problem should be important for the individual and the community. Diagnostic follow­up and intervention should be available to all who require them. There should be a favorable cost­benefit ratio. Public acceptance must be high. Scientific Scientific Natural history of the condition should be adequately understood. This knowledge permits identification of early stages of disease and appropriate biologic markers of progression. Prevalence of the disease or condition is high. Ethical Ethical 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 as well as acceptable, effective methods of prevention are available. Characteristics of a Good Screening Test Characteristics of a Good Screening Test Simple­­easy to learn and perform. Rapid­­quick to administer; results available rapidly. Inexpensive­­good cost­benefit ratio. Safe­­no harm to participants. Acceptable­­to target group. Evaluation of Screening Tests Evaluation of Screening Tests Reliability types Repeated measurements Internal consistency Interjudge Validity types Content Criterion­referenced Predictive Concurrent Construct Reliability (Precision) Reliability (Precision) The ability of a measuring instrument to give consistent results on repeated trials. Repeated measurement reliability­­the degree of consistency among repeated measurements of the same individual on more than one occasion. Reliability (cont’d) Reliability Internal consistency reliability­­evaluates the degree of agreement or homogeneity within a questionnaire measure of an attitude, personal characteristic, or psychologic attribute. Interjudge reliability­­reliability assessments derived from agreement among trained experts. Validity (Accuracy) Validity (Accuracy) The ability of a measuring instrument to give a true measure. Can be evaluated only if an accepted and independent method for confirming the test measurement exists. Validity (cont’d) Validity Content validity­­the degree to which a measure covers the range of meanings included within the concept. Criterion­referenced validity­­found by correlating a measure with an external criterion of the entity being assessed. Validity (cont’d) Validity Two types of criterion­referenced validity: Predictive validity­­denotes the ability of a measure to predict some attribute or characteristic in the future. Concurrent validity­­obtained by correlating a measure with an alternative measure of the same phenomenon taken at the same point in time. Validity (cont’d) Validity Construct Validity­­degree to which the measurement agrees with the theoretical concept being investigated. Representation of Reliability Representation of Reliability and Validity Sources of Unreliability and Invalidity Sources of Unreliability and Invalidity Measurement bias­­constant errors that are introduced by a faulty measuring device and tend to reduce the reliability of measurements. Example: A miscalibrated blood pressure manometer. Sources of Unreliability and Invalidity Sources of Unreliability and Invalidity (cont’d) Halo effect­­bias that affects the validity of questionnaire measurements. Social desirability effects Example: All items of a checklist evaluation of an employee may be filled out in the same general direction based on the supervisor’s opinion of the individual. Respondent answers questions in a manner that agrees with desirable social norms. Fourfold Table Fourfold Table Gold Standard Present Absent Test Result Positive Negative Total a c a + c b d b + d Total a + b c + d Measures of the Validity of Screening Measures of the Validity of Screening Tests Sensitivity­­the ability of the test to identify correctly all screened individuals who actually have the disease (a/a+c). Specificity­­the ability of the test to identify only nondiseased individuals who actually do not have the disease (d/b+d). Measures of the Validity of Measures of the Validity of Screening Tests (cont’d) Predictive value (+)­­the proportion of individuals screened positive by the test who actually have the disease (a/a+b). Predictive value (­)­­the proportion of individuals screened negative by the test who do not have the disease (d/c+d). Other Measures from the 2 by 2 Table Other Measures from the 2 by 2 Table Accuracy of a screening test­­determined by the formula: (a+d)/(a+b+c+d). Prevalence­­determined by the formula: (a+c)/(a+b+c+d) Sample Calculation Sample Calculation Effects of Disease Prevalence on the Effects of Disease Prevalence on the Predictive Value of a Screening Test When the prevalence of a disease falls, the predictive value (+) falls, and the predictive value (­) rises. Relationship Between Sensitivity Relationship Between Sensitivity and Specificity To improve sensitivity, the cut point used to classify individuals as diseased should be moved farther in the range of the nondiseased (normals). To improve specificity, the cut point should be moved farther in the range typically associated with the disease. Relationship (cont’d) Relationship Procedures to Improve Sensitivity Procedures to Improve Sensitivity and Specificity Retrain screeners­­reduces the amount of misclassification in tests that require human assessment. Recalibrate screening instrument­­reduces the amount of imprecision. Utilize a different test. Utilize more than one test. Evaluation of Screening Programs Evaluation of Screening Programs Randomized control trials Subjects receive either the new screening test or usual care. Compare geographic regions with screening programs to those without. Ecologic time trend studies Case­control studies Cases­­fatal cases of the disease. Controls­­nonfatal cases. Exposure­­screening program. Sources of Screening Evaluation Bias Sources of Screening Evaluation Bias Lead time bias The perception that the screen­detected case has longer survival because the disease was identified early. Length bias Particularly relevant to cancer screening. Tumors identified by screening are slower growing and have a better prognosis. Selection bias Motivated participants have a different probability of disease than do those who refuse to participate. Natural History of Disease Natural History of Disease Issues in the Classification of Issues in the Classification of Morbidity and Mortality The nomenclature and classification of disease are central to the reliable measurement of the outcome variable in epidemiologic research. Nomenclature­­a highly specific set of terms for describing and recording clinical or pathologic diagnoses to classify ill persons into groups. Issues in the Classification of Morbidity and Issues in the Classification of Morbidity and Mortality (cont’d) Classification­­the statistical compilation of groups of cases of disease by arranging disease entities into categories that share similar features. Two types of criteria used for the classification of ill persons: Causal Manifestational ...
View Full Document

  • Spring '08
  • Edmundson
  • Screening Tests, Screening Mass Screening, Screening Multiphasic Screening, Mass Health Examinations

{[ snackBarMessage ]}

Ask a homework question - tutors are online