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True Disease Status (true + disease_status)
Selected AbstractsAssessing accuracy of a continuous screening test in the presence of verification biasJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES C (APPLIED STATISTICS), Issue 1 2005Todd A. Alonzo Summary., In studies to assess the accuracy of a screening test, often definitive disease assessment is too invasive or expensive to be ascertained on all the study subjects. Although it may be more ethical or cost effective to ascertain the true disease status with a higher rate in study subjects where the screening test or additional information is suggestive of disease, estimates of accuracy can be biased in a study with such a design. This bias is known as verification bias. Verification bias correction methods that accommodate screening tests with binary or ordinal responses have been developed; however, no verification bias correction methods exist for tests with continuous results. We propose and compare imputation and reweighting bias-corrected estimators of true and false positive rates, receiver operating characteristic curves and area under the receiver operating characteristic curve for continuous tests. Distribution theory and simulation studies are used to compare the proposed estimators with respect to bias, relative efficiency and robustness to model misspecification. The bias correction estimators proposed are applied to data from a study of screening tests for neonatal hearing loss. [source] Optometric glaucoma referrals , measures of effectiveness and implications for screening strategyOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 6 2000Jim Gilchrist Summary The effectiveness of disease screening is conventionally evaluated using the epidemiological indices of sensitivity and specificity, which measure the association between screening test results and final diagnoses of all the patients screened. The effectiveness of optometric glaucoma referrals cannot be measured using such indices because diagnoses are obtained only on patients who are referred, while the true disease status of those not referred remains unknown. Instead, glaucoma referral effectiveness has been evaluated using measures of ,detection rate', the proportion of those screened who are correctly referred, and ,referral accuracy', the proportion of those referred who are correctly referred occurrence. Examination of these operational measures shows that their obtainable values and, hence, their interpretation are influenced by the total proportions of diseased and referred patients, one or both of which will generally be unavailable in evaluating samples of referrals. On the other hand, if valid estimates of these proportions can be obtained from other sources, it is possible to rescale detection rate and referral accuracy to take account of them. This rescaling produces a pair of weighted kappa coefficients, chance-corrected measures of association between referral and diagnosis, which provide a better indication of true referral effectiveness than other measures. An important consequence of this approach is that it provides a clear quantitative illustration of the need for a dual strategy to improve the overall quality of optometric glaucoma screening; widespread adoption of more comprehensive modes of screening to improve accuracy, together with a significant increase in the total numbers of patients screened to improve detection. In order for detection rates to reach desirable levels, the total number of referrals in any sub-population of patients must match or exceed the number of patients with disease. This analysis confirms quantitatively that which is intuitively obvious; not only that glaucoma awareness and uptake of screening opportunities must be encouraged in all patients over 40 years of age, but also that the older and/or more at risk patients are, the greater is their need to take advantage of glaucoma screening. [source] ESTIMATING THE FALSE NEGATIVE FRACTION FOR A MULTIPLE SCREENING TEST FOR BOWEL CANCER WHEN NEGATIVES ARE NOT VERIFIEDAUSTRALIAN & NEW ZEALAND JOURNAL OF STATISTICS, Issue 4 2004Chris J. Lloyd Summary This paper aims to estimate the false negative fraction of a multiple screening test for bowel cancer, where those who give negative results for six consecutive tests do not have their true disease status verified. A subset of these same individuals is given a further screening test, for the sole purpose of evaluating the accuracy of the primary test. This paper proposes a beta heterogeneity model for the probability of a diseased individual ,testing positive' on any single test, and it examines the consequences of this model for inference on the false negative fraction. The method can be generalized to the case where selection for further testing is informative, though this did not appear to be the case for the bowel-cancer data. [source] Comparing Accuracy in an Unpaired Post-market Device Study with Incomplete Disease AssessmentBIOMETRICAL JOURNAL, Issue 3 2009Todd A. Alonzo Abstract The sensitivity and specificity of a new medical device are often compared relative to that of an existing device by calculating ratios of sensitivities and specificities. Although it would be ideal for all study subjects to receive the gold standard so true disease status was known for all subjects, it is often not feasible or ethical to obtain disease status for everyone. This paper proposes two unpaired designs where each subject is only administered one of the devices and device results dictate which subjects are to receive disease verification. Estimators of the ratio of accuracy and corresponding confidence intervals are proposed for these designs as well as sample size formulae. Simulation studies are performed to investigate the small sample bias of the estimators and the performance of the variance estimators and sample size formulae. The sample size formulae are applied to the design of a cervical cancer study to compare the accuracy of a new device with the conventional Pap smear. [source] | ||||||||||