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Disease Assessment (disease + assessment)

Distribution by Scientific Domains
Mathematics and Statistics40%
Life Sciences40%

Terms modified by Disease Assessment

  • disease assessment scale
    		•

    Selected Abstracts

    Comparing Accuracy in an Unpaired Post-market Device Study with Incomplete Disease Assessment

    BIOMETRICAL JOURNAL, Issue 3 2009
    Todd 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]

    Assessing accuracy of a continuous screening test in the presence of verification bias

    JOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES C (APPLIED STATISTICS), Issue 1 2005
    Todd 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]

    Weather-based prediction of anthracnose severity using artificial neural network models

    PLANT PATHOLOGY, Issue 4 2004
    S. Chakraborty
    Data were collected and analysed from seven field sites in Australia, Brazil and Colombia on weather conditions and the severity of anthracnose disease of the tropical pasture legume Stylosanthes scabra caused by Colletotrichum gloeosporioides. Disease severity and weather data were analysed using artificial neural network (ANN) models developed using data from some or all field sites in Australia and/or South America to predict severity at other sites. Three series of models were developed using different weather summaries. Of these, ANN models with weather for the day of disease assessment and the previous 24 h period had the highest prediction success, and models trained on data from all sites within one continent correctly predicted disease severity in the other continent on more than 75% of days; the overall prediction error was 21·9% for the Australian and 22·1% for the South American model. Of the six cross-continent ANN models trained on pooled data for five sites from two continents to predict severity for the remaining sixth site, the model developed without data from Planaltina in Brazil was the most accurate, with >85% prediction success, and the model without Carimagua in Colombia was the least accurate, with only 54% success. In common with multiple regression models, moisture-related variables such as rain, leaf surface wetness and variables that influence moisture availability such as radiation and wind on the day of disease severity assessment or the day before assessment were the most important weather variables in all ANN models. A set of weights from the ANN models was used to calculate the overall risk of anthracnose for the various sites. Sites with high and low anthracnose risk are present in both continents, and weather conditions at centres of diversity in Brazil and Colombia do not appear to be more conducive than conditions in Australia to serious anthracnose development. [source]

    Progress, spread and natural transmission of Bahia bark scaling of citrus in Brazil

    ANNALS OF APPLIED BIOLOGY, Issue 3 2006
    F.F. Laranjeira
    Abstract Progress, spread and natural transmission of Bahia bark scaling of citrus were evaluated in a trial where 240 screenhouse-nursed nucellar grapefruit plants ,,Clason', ,Little River Seedless', ,Red Blush', ,Reed' and ,Howell Seedless' cvs , were planted alongside and 5 m apart from a 10-year-old symptomatic ,Marsh Seedless' grapefruit orchard. Plants were distributed in 16 rows of 15 trees, with three plants of each cultivar per row. Eight trial plants were kept in screen cages. Incidence of symptomatic plants was assessed at 3-months intervals, for 5 years, and for further 2 years at irregular intervals. Cumulative maps of disease incidence were produced for each assessment date and used in all analyses. Temporal progress was analysed by nonlinear fitting of three disease progress models. Spread was characterised in three levels of spatial hierarchy by the following analyses: ordinary runs, binomial dispersion index, binary power law fitting, isopath mapping and nonlinear fitting of disease gradient models. The first symptomatic plant was detected 2 years after planting. In the last disease assessment, 5 years after the first, 98% of the unprotected plants were symptomatic. None of the screen-caged trees showed any symptoms. Bahia bark scaling progress was polyetic and best described by the logistic model. Ordinary runs analysis showed little if any evidence of transmission between adjacent trees. Diseased plants showed a very aggregated pattern inside quadrats (D > 5 and b > 1.53). Isopath mapping showed that main spread was only because of the primary inoculum source. Secondary foci were also observed, but they were never dissociated from main initial disease focus. Disease gradient followed wind direction, starting near the original inoculum source and was best described by exponential model. These results support a hypothesis of Bahia bark scaling transmission by air-borne vectors with limited dispersion ability. [source]

    Phase II study of daily oral perifosine in patients with advanced soft tissue sarcoma,

    CANCER, Issue 10 2006
    Howard H. Bailey MD
    Abstract BACKGROUND. A multicenter Phase II study was performed to evaluate the clinical activity of an initial loading (150 mg every 6 hours × 4 doses) dose followed by continuous daily oral dosing (100 mg/day) of perifosine in patients with advanced soft tissue sarcomas (STSs). METHODS. Patients with measurable metastatic STS received perifosine as first-, second-, or third-line treatment and underwent disease assessment every 8 weeks until disease progression, excessive toxicity, or patient refusal. RESULTS. Twenty-three patients received 66 cycles (1 cycle = 4 weeks) of perifosine. One partial response of 9 months duration was observed. The overall 3 and 6 month progression-free survival was 22% and 9%. NCI CTC (v2.0) Grade 1 to 2 gastrointestinal toxicity or fatigue were the most common (>50% of subjects) toxicities observed. The steady-state plasma perifosine levels (Css) were similar to prior experience (mean 6 ,g/mL). Patients with Css levels >6 ,g/mL appeared more likely to remain on study past 2 months than those with levels <6 ,g/mL. CONCLUSIONS. Despite not achieving the primary objective of ,40% 6-month progression-free survival rate, optimism remains for this agent in STS patients. Prolonged responses in heavily pretreated STS patients continue to be observed with perifosine treatment. Continued assessment of perifosine in STS appears warranted, with special attention to specific histologies or tumor characteristics that might identify a more sensitive population and achieving perifosine Css levels >6 ,g/mL. Cancer 2006 © 2006 American Cancer Society. [source]