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PCR colorimetric dot-blot assay and clinical pretest probability for diagnosis of Pulmonary Tuberculosis in Smear-Negative patients

Scherer, Luciene ; Sperhacke, Rosa ; Jarczewski, Carla ; Cafrune, Patrícia I; Minghelli, Simone ; Ribeiro, Marta ; Mello, Fernanda CQ; Ruffino-Netto, Antonio ; Rossetti, Maria LR; Kritski, Afrânio L
Fonte: Biblioteca Digital da Produção Intelectual da USP Publicador: Biblioteca Digital da Produção Intelectual da USP
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
46.75%
Abstract Background Smear-negative pulmonary tuberculosis (SNPTB) accounts for 30% of Pulmonary Tuberculosis (PTB) cases reported annually in developing nations. Polymerase chain reaction (PCR) may provide an alternative for the rapid detection of Mycobacterium tuberculosis (MTB); however little data are available regarding the clinical utility of PCR in SNPTB, in a setting with a high burden of TB/HIV co-infection. Methods To evaluate the performance of the PCR dot-blot in parallel with pretest probability (Clinical Suspicion) in patients suspected of having SNPTB, a prospective study of 213 individuals with clinical and radiological suspicion of SNPTB was carried out from May 2003 to May 2004, in a TB/HIV reference hospital. Respiratory specialists estimated the pretest probability of active disease into high, intermediate, low categories. Expectorated sputum was examined by direct microscopy (Ziehl-Neelsen staining), culture (Lowenstein Jensen) and PCR dot-blot. Gold standard was based on culture positivity combined with the clinical definition of PTB. Results In smear-negative and HIV subjects...

Avaliação da técnica de PCR in house no diagnóstico de tuberculose pulmonar

Scherer, Luciene Cardoso
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Tese de Doutorado Formato: application/pdf
POR
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26.31%
Objetivos: Avaliar o desempenho e o custo-efetividade de duas técnicas de PCR (Polymerase Chain Reaction) in house: PCR dot-blot e o PCR utilizando a eletroforese em gel de agarose (PCR-AG) no diagnóstico de Tuberculose Pulmonar em pacientes infectados ou não pelo HIV . Material e Métodos: Um estudo prospectivo foi conduzido (de Maio de 2003 a Maio de 2004) em um Hospital de Referência para TB/HIV. Escarros de 277 indivíduos com suspeita de Tuberculose Pulmonar (PTB) foram testados pelas técnicas de microscopia direta pela coloração de Ziehl-Neelsen (ZN), cultura e pelas metodologias de PCR in house (PCR dot-blot e PCR-AG). A acurácia dos testes foi avaliada de acordo com o status de HIV, com o status de tratamento prévio ou não, e com a estimativa de probabilidade pré-teste feita pelos pneumologistas. O padrão ouro utilizado foi a cultura positiva combinada com a definição clínica de PTB (usando sintomas, fatores de risco e Raios-X). O custo efetividade foi expresso por: a) custo por correto caso diagnosticado de Tuberculose; b) custo por correto caso diagnosticado de Tuberculose e tratado incluindo tratamento de casos falsamente diagnosticados; c) custo por casos incorretamente diagnosticados e não tratados. Resultados: Prevalência de PTB foi 46...

Practical Implementation of a Multiplex PCR for Acute Respiratory Tract Infections in Children

Gruteke, Paul; Glas, Afina S.; Dierdorp, Mirjam; Vreede, Willem B.; Pilon, Jan-Willem; Bruisten, Sylvia M.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /12/2004 EN
Relevância na Pesquisa
26.31%
Molecular testing for acute respiratory infections (ARIs) has documented value but limited implementation due to questions that typically slow the acceptance of new tests. This study sought to address these questions and achieve implementation. Rhinovirus was added to a nested multiplex PCR (M-PCR), increasing its diagnostic yield. Over one winter, three hospital pediatric departments used the M-PCR to complement their direct fluorescent-antibody assay (DFA) for respiratory syncytial virus (RSV). Clinicians recorded “pretest probability estimates” (using continuous scales for various pathogen groups) for comparison with test results; treatments and test turnaround times were also recorded. Transnasal and throat swabs, with or without nasopharyngeal aspirate (NPA), were M-PCR tested. NPA-containing sample sets found to be RSV positive by DFA were not further tested. Single PCR for human metapneumovirus (hMPV) was performed retrospectively. Of 178 ARI episodes representing 172 patients, NPA was included in 97 sample sets; 54 (56%) were determined to be RSV positive. The other NPA-containing sample sets (n = 43) yielded 27 findings (63%), and the swab-only sets (n = 81) yielded 47 findings (58%); rhinovirus was found most often. Testing for hMPV yielded seven positive results. M-PCR median turnaround times were 4 days in swab-only samples and 5 days with NPA. Antibiotics were prescribed in 50 episodes...

Iron deficiency anemia in the elderly: the diagnostic process.

Patterson, C; Guyatt, G H; Singer, J; Ali, M; Turpie, I
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/02/1991 EN
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26.69%
OBJECTIVE: To determine the effectiveness of physician probability estimates calculated on the basis of findings from history-taking and physical examination in the diagnosis of iron deficiency anemia in elderly patients. DESIGN: Prospective study. SETTING: Two community hospitals offering secondary and tertiary care. PATIENTS: A total of 259 patients over 65 years of age found to have previously undiagnosed anemia. MEASURES: Physician estimates of the likelihood of iron deficiency before (pretest probability) and after (post-test probability) the laboratory test results were available. The hemogram was available to the physicians when they made their pretest probability estimates. Because the serum ferritin level proved to be the most powerful of the laboratory test results studied, the likelihood ratios associated with the post-test estimates were compared with the ratios associated with the serum ferritin level. MAIN RESULTS: The post-test probability estimates were influenced by the serum ferritin level and the pretest estimates. The post-test estimates derived from the findings obtained through history-taking and physical examination and the laboratory test results (including the serum ferritin level) were slightly less accurate in predicting iron deficiency than the serum ferritin level alone. Nevertheless...

Diagnosis and treatment of deep-vein thrombosis

Scarvelis, Dimitrios; Wells, Philip S.
Fonte: Canadian Medical Association Publicador: Canadian Medical Association
Tipo: Artigo de Revista Científica
Publicado em 24/10/2006 EN
Relevância na Pesquisa
26.31%
Deep-vein thrombosis (DVT) is a common condition that can lead to complications such as postphlebitic syndrome, pulmonary embolism and death. The approach to the diagnosis of DVT has evolved over the years. Currently an algorithm strategy combining pretest probability, D-dimer testing and compression ultrasound imaging allows for safe and convenient investigation of suspected lower-extremity thrombosis. Patients with low pretest probability and a negative D-dimer test result can have proximal DVT excluded without the need for diagnostic imaging. The mainstay of treatment of DVT is anticoagulation therapy, whereas interventions such as thrombolysis and placement of inferior vena cava filters are reserved for special situations. The use of low-molecular-weight heparin allows for outpatient management of most patients with DVT. The duration of anticoagulation therapy depends on whether the primary event was idiopathic or secondary to a transient risk factor. More research is required to optimally define the factors that predict an increased risk of recurrent DVT to determine which patients can benefit from extended anticoagulant therapy.

Interpretation of diagnostic data: 5. How to do it with simple maths.

Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/11/1983 EN
Relevância na Pesquisa
26.41%
The use of simple maths with the likelihood ratio strategy fits in nicely with our clinical views. By making the most out of the entire range of diagnostic test results (i.e., several levels, each with its own likelihood ratio, rather than a single cut-off point and a single ratio) and by permitting us to keep track of the likelihood that a patient has the target disorder at each point along the diagnostic sequence, this strategy allows us to place patients at an extremely high or an extremely low likelihood of disease. Thus, the numbers of patients with ultimately false-positive results (who suffer the slings of labelling and the arrows of needless therapy) and of those with ultimately false-negative results (who therefore miss their chance for diagnosis and, possibly, efficacious therapy) will be dramatically reduced. The following guidelines will be useful in interpreting signs, symptoms and laboratory tests with the likelihood ratio strategy: Seek out, and demand from the clinical or laboratory experts who ought to know, the likelihood ratios for key symptoms and signs, and several levels (rather than just the positive and negative results) of diagnostic test results. Identify, when feasible, the logical sequence of diagnostic tests. Estimate the pretest probability of disease for the patient...

Likelihood ratios: Clinical application in day-to-day practice

Parikh, Rajul; Parikh, Shefali; Arun, Ellen; Thomas, Ravi
Fonte: Medknow Publications Publicador: Medknow Publications
Tipo: Artigo de Revista Científica
Publicado em //2009 EN
Relevância na Pesquisa
26.31%
In this article we provide an introduction to the use of likelihood ratios in clinical ophthalmology. Likelihood ratios permit the best use of clinical test results to establish diagnoses for the individual patient. Examples and step-by-step calculations demonstrate the estimation of pretest probability, pretest odds, and calculation of posttest odds and posttest probability using likelihood ratios. The benefits and limitations of this approach are discussed.

A Clinical Scoring System for Selection of Patients for PTEN Mutation Testing Is Proposed on the Basis of a Prospective Study of 3042 Probands

Tan, Min-Han; Mester, Jessica; Peterson, Charissa; Yang, Yiran; Chen, Jin-Lian; Rybicki, Lisa A.; Milas, Kresimira; Pederson, Holly; Remzi, Berna; Orloff, Mohammed S.; Eng, Charis
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em 07/01/2011 EN
Relevância na Pesquisa
26.31%
Cowden syndrome (CS) and Bannayan-Riley-Ruvalcaba syndrome are allelic, defined by germline PTEN mutations, and collectively referred to as PTEN hamartoma tumor syndrome. To date, there are no existing criteria based on large prospective patient cohorts to select patients for PTEN mutation testing. To address these issues, we conducted a multicenter prospective study in which 3042 probands satisfying relaxed CS clinical criteria were accrued. PTEN mutation scanning, including promoter and large deletion analysis, was performed for all subjects. Pathogenic mutations were identified in 290 individuals (9.5%). To evaluate clinical phenotype and PTEN genotype against protein expression, we performed immunoblotting (PTEN, P-AKT1, P-MAPK1/2) for a patient subset (n = 423). In order to obtain an individualized estimation of pretest probability of germline PTEN mutation, we developed an optimized clinical practice model to identify adult and pediatric patients. For adults, a semiquantitative score—the Cleveland Clinic (CC) score—resulted in a well-calibrated estimation of pretest probability of PTEN status. Overall, decreased PTEN protein expression correlated with PTEN mutation status; decreasing PTEN protein expression correlated with increasing CC score (p < 0.001)...

Renal angina: concept and development of pretest probability assessment in acute kidney injury

Chawla, Lakhmir S; Goldstein, Stuart L; Kellum, John A; Ronco, Claudio
Fonte: BioMed Central Publicador: BioMed Central
Tipo: Artigo de Revista Científica
EN
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46.5%
The context of a diagnostic test is a critical component for the interpretation of its result. This context defines the pretest probability of the diagnosis and forms the basis for the interpretation and value of adding the diagnostic test. In the field of acute kidney injury, a multitude of early diagnostic biomarkers have been developed, but utilization in the appropriate context is less well understood and has not been codified until recently. In order to better operationalize the context and pretest probability assessment for acute kidney injury diagnosis, the renal angina concept was proposed in 2010 for use in both children and adults. Renal angina has been assessed in approximately 1,000 subjects. However, renal angina as a concept is still unfamiliar to most clinicians and the rationale for introducing the term is not obvious. We therefore review the concept and development of renal angina, and the currently available data validating it. We discuss the various arguments for and against this construct. Future research testing the performance of renal angina with acute kidney injury biomarkers is warranted.

Clinical judgment to estimate pretest probability in the diagnosis of Cushing's syndrome under a Bayesian perspective; Contribuição do julgamento clínico na estimativa da probabilidade pré-teste do diagnóstico da síndrome de Cushing sob a perspectiva Bayesiana

Cipoli, Daniel Eduardo; Martinez, Edson Zangiacomi; Castro, Margaret de; Moreira, Ayrton Custodio
Fonte: Sociedade Brasileira de Endocrinologia e Metabologia; SÃO PAULO Publicador: Sociedade Brasileira de Endocrinologia e Metabologia; SÃO PAULO
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.76%
OBJECTIVE: To estimate the pretest probability of Cushing's syndrome (CS) diagnosis by a Bayesian approach using intuitive clinical judgment. MATERIALS AND METHODS: Physicians were requested, in seven endocrinology meetings, to answer three questions: "Based on your personal expertise, after obtaining clinical history and physical examination, without using laboratorial tests, what is your probability of diagnosing Cushing's Syndrome?"; "For how long have you been practicing Endocrinology?"; and "Where do you work?". A Bayesian beta regression, using the WinBugs software was employed. RESULTS: We obtained 294 questionnaires. The mean pretest probability of CS diagnosis was 51.6% (95%CI: 48.7-54.3). The probability was directly related to experience in endocrinology, but not with the place of work. CONCLUSION: Pretest probability of CS diagnosis was estimated using a Bayesian methodology. Although pretest likelihood can be context-dependent, experience based on years of practice may help the practitioner to diagnosis CS. Arq Bras Endocrinol Metab. 2012;56(9):633-7

Clinical judgment to estimate pretest probability in the diagnosis of Cushing's syndrome under a Bayesian perspective

Cipoli,Daniel E.; Martinez,Edson Z.; Castro,Margaret de; Moreira,Ayrton C.
Fonte: Sociedade Brasileira de Endocrinologia e Metabologia Publicador: Sociedade Brasileira de Endocrinologia e Metabologia
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2012 EN
Relevância na Pesquisa
66.76%
OBJECTIVE: To estimate the pretest probability of Cushing's syndrome (CS) diagnosis by a Bayesian approach using intuitive clinical judgment. MATERIALS AND METHODS: Physicians were requested, in seven endocrinology meetings, to answer three questions: "Based on your personal expertise, after obtaining clinical history and physical examination, without using laboratorial tests, what is your probability of diagnosing Cushing's Syndrome?"; "For how long have you been practicing Endocrinology?"; and "Where do you work?". A Bayesian beta regression, using the WinBugs software was employed. RESULTS: We obtained 294 questionnaires. The mean pretest probability of CS diagnosis was 51.6% (95%CI: 48.7-54.3). The probability was directly related to experience in endocrinology, but not with the place of work. CONCLUSION: Pretest probability of CS diagnosis was estimated using a Bayesian methodology. Although pretest likelihood can be context-dependent, experience based on years of practice may help the practitioner to diagnosis CS. Arq Bras Endocrinol Metab. 2012;56(9):633-7

Utilidad del dímero D en el diagnóstico de tromboembolismo pulmonar en la Fundación Santa Fé de Bogotá

Rodriguez Lima, David Rene; Prada Romero, Leidy Paola; Pinzón, Bibiana; Beltran, Johnny
Fonte: Facultad de Medicina Publicador: Facultad de Medicina
Tipo: info:eu-repo/semantics/bachelorThesis; info:eu-repo/semantics/acceptedVersion Formato: application/pdf
Publicado em 02/12/2011 SPA
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26.46%
INTRODUCCIÓN: El diagnóstico de Tromboembolismo Pulmonar (TEP) ha sido un reto clínico a pesar de los avances en modalidades diagnósticas y opciones terapéuticas, el TEP permanece como una entidad sub diagnosticada y letal. La medición en sangre del Dímero D, con punto de corte de 500 mcg/L, por lo tanto es una excelente prueba de tamizaje para los pacientes en el departamento de urgencias . Esta evaluación inicial debe ser complementada con la realización de angioTAC de tórax, decisión que debe ser tomada precozmente con el fin de evitar complicaciones que amenacen la vida METODOLOGIA: Se realizo un estudio de prueba diagnóstica retrospectivo donde se revisaron las historias clínicas de 109 pacientes adultos de la Fundación Santa Fe de Bogotá en quienes se realizo angioTAC de tórax con protocolo para TEP, con probabilidad diagnóstica de Tromboembolismo Pulmonar Baja o Intermedia por criterios de Wells y que además tengan Dímero D. Se calculo la sensibilidad y especificidad del Dímero D teniendo en cuenta la probabilidad clínica pre test calculada por criterios de Wells, y se calcularon likelihood ratio positivo y negativo para cada punto de corte de Dímero D. RESULTADOS: El estudio mostro una sensibilidad del 100% para valores de Dímero D menores de 1100 mcg/L...

Cost effectiveness of alternative imaging strategies for the diagnosis of small-bowel crohn's disease

Levesque, Barrett G.; Cipriano, Lauren E.; Chang, Steven L.; Lee, Keane K.; Owens, Douglas K.; Garber, Alan M
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
26.62%
Background & Aims The cost effectiveness of alternative approaches to the diagnosis of small-bowel Crohn's disease is unknown. This study evaluates whether computed tomographic enterography (CTE) is a cost-effective alternative to small-bowel follow-through (SBFT) and whether capsule endoscopy is a cost-effective third test in patients in whom a high suspicion of disease remains after 2 previous negative tests. Methods A decision-analytic model was developed to compare the lifetime costs and benefits of each diagnostic strategy. Patients were considered with low (20%) and high (75%) pretest probability of small-bowel Crohn's disease. Effectiveness was measured in quality-adjusted life-years (QALYs) gained. Parameter assumptions were tested with sensitivity analyses. Results With a moderate to high pretest probability of small-bowel Crohn's disease, and a higher likelihood of isolated jejunal disease, follow-up evaluation with CTE has an incremental cost-effectiveness ratio of less than $54,000/QALY-gained compared with SBFT. The addition of capsule endoscopy after ileocolonoscopy and negative CTE or SBFT costs greater than $500,000 per QALY-gained in all scenarios. Results were not sensitive to costs of tests or complications but were sensitive to test accuracies. Conclusions The cost effectiveness of strategies depends critically on the pretest probability of Crohn's disease and if the terminal ileum is examined at ileocolonoscopy. CTE is a cost-effective alternative to SBFT in patients with moderate to high suspicion of small-bowel Crohn's disease. The addition of capsule endoscopy as a third test is not a cost-effective third test...

Post-test probability that men in the community with raised plasma ferritin concentrations are hazardous drinkers.

Peach, H G; Bath, N E
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1999 EN
Relevância na Pesquisa
36.58%
BACKGROUND: Raised plasma ferritin concentrations occur unexpectedly during iron studies done by primary care physicians. Plasma ferritin concentration has been positively associated with alcohol use among men. AIM: To determine the post-test probability that men in the community with raised plasma ferritin concentrations are hazardous drinkers. METHODS: The subjects were 152 men, randomly selected from a city's electoral roll. Nineteen (12.5 (2.7)%, mean (SEM)) admitted to drinking hazardously. The pretest probability of a man being a hazardous drinker was 0.125. This was converted to pretest odds of 0.14. The likelihood ratio (the ratio of the probability of obtaining a raised plasma ferritin concentration in a hazardous drinker (sensitivity) to the probability of obtaining a raised plasma ferritin concentration in a non-hazardous drinker (1-specificity)) was calculated for different plasma ferritin cut off points. RESULTS: A plasma ferritin level of > 652 micrograms/l gave the largest likelihood ratio, 4.16. Post-test odds were obtained by multiplying the pretest odds (0.14) by the likelihood ratio (4.16). A plasma ferritin level of > 652 micrograms/l had a post-test odds for a man being a hazardous drinker of 0.58. This was converted to a post-test probability of 0.37. CONCLUSIONS: Inquiries could usefully be made into the alcohol consumption of men with a plasma ferritin concentration > 652 micrograms/l...

Effect of a Patient's Psychiatric History on Physicians' Estimation of Probability of Disease

Graber, Mark A; Bergus, George; Dawson, Jeffrey D; Wood, G Blake; Levy, Barcey T; Levin, Irwin
Fonte: Blackwell Science Inc Publicador: Blackwell Science Inc
Tipo: Artigo de Revista Científica
Publicado em /03/2000 EN
Relevância na Pesquisa
36.14%
A questionnaire was mailed to 300 Iowa family physicians to determine the influence of a prior psychiatric history on decision making. The response rate was 77%. Respondents were less likely to believe that a patient had serious illness when presenting with a severe headache or abdominal pain if the patient had a prior history of depression ( P < .05) or prior history of somatic complaints ( P < .05), compared with a patient with no past history. Respondents were less likely to report that they would order testing for a patient with headache or abdominal pain if the patient had a history of depression ( P < .05, P = .08, respectively) or somatic complaints ( P < .01). Differences in likelihood of ordering tests were not significant after adjusting for differences in estimated probability of disease. We conclude that physicians respond differently to patients with psychiatric illness because of their estimation of pretest probability of disease rather than bias. We conclude that past psychiatric history influences physicians' estimation of disease presence and willingness to order tests.

Investigation of Suspected Pulmonary Embolism at Hutt Valley Hospital with CT Pulmonary Angiography: Current Practice and Opportunities for Improvement

Kennedy, Nick; Jayathissa, Sisira; Healy, Paul
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
26.44%
Aims. To study the use of CT pulmonary angiography (CTPA) at Hutt Hospital and investigate the use of pretest probability scoring in the assessment of patients with suspected pulmonary embolism (PE). Methods. We studied patients with suspected PE that underwent CTPA between January and May 2012 and collected data on demographics, use of pretest probability scoring, and use of D Dimer and compared our practice with the British Thoracic Society (BTS) guideline. Results. 105 patients underwent CTPA and 15% of patients had PE. 13% of patients had a Wells score prior to their scan. Wells score calculated by researchers revealed 54%, 36%, and 8% patients had low, medium, and high risk pretest probabilities and 8%, 20%, and 50% of these patients had positive scans. D Dimer was performed in 58% of patients and no patients with a negative D Dimer had a PE. Conclusion. The CTPA positive rate was similar to other contemporary studies but lower than previous New Zealand studies and some international guidelines. Risk stratification of suspected PE using Wells score and D Dimer was underutilised. A number of scans could have been safely avoided by using accepted guidelines reducing resources use and improving patient safety.

The impact of a Hausman pretest on the coverage probability and expected length of confidence intervals

Kabaila, Paul; Mainzer, Rheanna; Farchione, Davide
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/06/2015
Relevância na Pesquisa
26.58%
In the analysis of clustered and longitudinal data, which includes a covariate that varies both between and within clusters (e.g. time-varying covariate in longitudinal data), a Hausman pretest is commonly used to decide whether subsequent inference is made using the linear random intercept model or the fixed effects model. We assess the effect of this pretest on the coverage probability and expected length of a confidence interval for the slope parameter. Our results show that for the small levels of significance of the Hausman pretest commonly used in applications, the minimum coverage probability of this confidence interval can be far below nominal. Furthermore, the expected length of this confidence interval is, on average, larger than the expected length of a confidence interval for the slope parameter based on the fixed effects model with the same minimum coverage.; Comment: arXiv admin note: substantial text overlap with arXiv:1412.5262

Dynamic Models of Learning and Education Measurement

Bao, Lei
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
26.37%
Pre-post testing is a commonly used method in physics education community for evaluating students' achievement and or the effectiveness of teaching through a specific period of instruction. A popular method to analyze pre-post testing results is the normalized gain first brought to the physics education community in wide use by R.R. Hake. This paper presents a measurement based probabilistic model of the dynamic process of learning that explains the experimentally observed features of the normalized gain. In Hake's study with thousands of students' pre-post testing results, he observed that on average 48 courses employing "interactive engagement" types of instruction achieved average normalized gains about two standard deviations greater than did 14 courses subjected to traditional instruction. For all courses the average normalized gains had a very low correlation +0.02 with average pretest scores. This feature of the normalized gain has allowed researchers to investigate the effectiveness of instruction using data collected from classes with widely different average pretest scores. However, the question of why the average normalized gain has this feature and to what extent this feature is generally present is not well understood. In addition...

The impact of a Hausman pretest, applied to panel data, on the coverage probability of confidence intervals

Kabaila, Paul; Mainzer, Rheanna; Farchione, Davide
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
26.67%
In the analysis of panel data that includes a time-varying covariate, a Hausman pretest is commonly used to decide whether subsequent inference is made using the random effects model or the fixed effects model. We consider the effect of this pretest on the coverage probability of a confidence interval for the slope parameter. We prove three new finite sample theorems that make it easy to assess, for a wide variety of circumstances, the effect of the Hausman pretest on the minimum coverage probability of this confidence interval. Our results show that for the small levels of significance of the Hausman pretest commonly used in applications, the minimum coverage probability of the confidence interval for the slope parameter can be far below nominal.; Comment: The exposition has been improved

Sensitivity and specificity of typhoid fever rapid antibody tests for laboratory diagnosis at two sub-Saharan African sites

Keddy,Karen H; Sooka,Arvinda; Letsoalo,Maupi E; Hoyland,Greta; Chaignat,Claire Lise; Morrissey,Anne B; Crump,John A
Fonte: World Health Organization Publicador: World Health Organization
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2011 EN
Relevância na Pesquisa
26.58%
OBJECTIVE: To evaluate three commercial typhoid rapid antibody tests for Salmonella Typhi antibodies in patients suspected of having typhoid fever in Mpumalanga, South Africa, and Moshi, United Republic of Tanzania. METHODS: The diagnostic accuracy of Cromotest® (semiquantitative slide agglutination and single tube Widal test),TUBEX®and Typhidot® was assessed against that of blood culture. Performance was modelled for scenarios with pretest probabilities of 5% and 50%. FINDINGS: In total 92 patients enrolled: 53 (57.6%) from South Africa and 39 (42.4%) from the United Republic of Tanzania. Salmonella Typhi was isolated from the blood of 28 (30.4%) patients. The semiquantitative slide agglutination and single-tube Widal tests had positive predictive values (PPVs) of 25.0% (95% confidence interval, CI: 0.6-80.6) and 20.0% (95% CI: 2.5-55.6), respectively. The newer typhoid rapid antibody tests had comparable PPVs: TUBEX®, 54.1% (95% CI: 36.9-70.5); Typhidot® IgM, 56.7% (95% CI: 37.4-74.5); and Typhidot® IgG, 54.3% (95% CI: 36.6-71.2). For a pretest probability of 5%, PPVs were: TUBEX®, 11.0% (95% CI: 6.6-17.9); Typhidot® IgM, 9.1% (95% CI: 5.8-14.0); and Typhidot® IgG, 11.0% (6.3-18.4). For a pretest probability of 50%, PPVs were: TUBEX®...