3,370 research outputs found
Bivariate analysis of sensitivity and specificity produces informative summary measures in diagnostic reviews
No full textBACKGROUND AND OBJECTIVES: Studies of diagnostic accuracy most often report pairs
of sensitivity and specificity. We demonstrate the advantage of using bivariate
meta-regression models to analyze such data.
METHODS: We discuss the methodology of both the summary Receiver Operating
Characteristic (sROC) and the bivariate approach by reanalyzing the data of a
published meta-analysis.
RESULTS: The sROC approach is the standard method for meta-analyzing diagnostic
studies reporting pairs of sensitivity and specificity. This method uses the
diagnostic odds ratio as the main outcome measure, which removes the effect of a
possible threshold but at the same time loses relevant clinical information about
test performance. The bivariate approach preserves the two-dimensional nature of
the original data. Pairs of sensitivity and specificity are jointly analyzed,
incorporating any correlation that might exist between these two measures using a
random effects approach. Explanatory variables can be added to the bivariate
model and lead to separate effects on sensitivity and specificity, rather than a
net effect on the odds ratio scale as in the sROC approach. The statistical
properties of the bivariate model are sound and flexible.
CONCLUSION: The bivariate model can be seen as an improvement and extension of
the traditional sROC approach
Meta-analysis and meta-modelling for diagnostic problems
No full textBackgroundA proportional hazards measure is suggested in the context of analyzing SROC curves that arise in the meta–analysis of diagnostic studies. The measure can be motivated as a special model: the Lehmann model for ROC curves. The Lehmann model involves study–specific sensitivities and specificities and a diagnostic accuracy parameter which connects the two.MethodsA study–specific model is estimated for each study, and the resulting study-specific estimate of diagnostic accuracy is taken as an outcome measure for a mixed model with a random study effect and other study-level covariates as fixed effects. The variance component model becomes estimable by deriving within-study variances, depending on the outcome measure of choice. In contrast to existing approaches – usually of bivariate nature for the outcome measures – the suggested approach is univariate and, hence, allows easily the application of conventional mixed modelling.ResultsSome simple modifications in the SAS procedure proc mixed allow the fitting of mixed models for meta-analytic data from diagnostic studies. The methodology is illustrated with several meta–analytic diagnostic data sets, including a meta–analysis of the Mini–Mental State Examination as a diagnostic device for dementia and mild cognitive impairment.ConclusionsThe proposed methodology allows us to embed the meta-analysis of diagnostic studies into the well–developed area of mixed modelling. Different outcome measures, specifically from the perspective of whether a local or a global measure of diagnostic accuracy should be applied, are discussed as well. In particular, variation in cut-off value is discussed together with recommendations on choosing the best cut-off value. We also show how this problem can be addressed with the proposed methodology
An electronic nose discriminates exhaled breath of patients with untreated Pulmonary Sarcoidosis from controls
No full textBackground: Sarcoidosis is a systemic granulomatous disease of unknown cause that affects the lungs in over 90% of cases. Breath analysis by electronic nose technology provides exhaled molecular profiles that have potential in the diagnosis of several respiratory diseases. Objectives: We hypothesized that exhaled molecular profiling may distinguish well-characterized patients with sarcoidosis from controls. To that end we performed electronic nose measurements in untreated and treated sarcoidosis patients and in healthy controls. Methods: 31 sarcoidosis patients (11 patients with untreated pulmonary sarcoidosis [age: 48.4 +/- 9.0], 20 patients with treated pulmonary sarcoidosis [age: 49.7 +/- 7.9]) and 25 healthy controls (age: 39.6 +/- 14.1) participated in a cross-sectional study. Exhaled breath was collected twice using a Tedlar bag by a standardized method. Both bags were then sampled by an electronic nose (Cyranose C320), resulting in duplicate data. Statistical analysis on sensor responses was performed off-line by principal components (PC) analyses, discriminant analysis and ROC curves. Results: Breathprints from patients with untreated pulmonary sarcoidosis were discriminated from healthy controls (CVA: 83.3%; AUC 0.825). Repeated measurements confirmed those results. Patients with untreated and treated sarcoidosis could be less well discriminated (CVA 74.2%), whereas the treated sarcoidosis group was undistinguishable from controls (CVA 66.7%) Conclusion: Untreated patients with active sarcoidosis can be discriminated from healthy controls. This suggests that exhaled breath analysis has potential for diagnosis and/or monitoring of sarcoidosis. (C) 2013 Elsevier Ltd. All rights reserved
Malaria knowledge and utilization of chemoprophylaxis in the UK population and in UK passengers departing to malaria-endemic areas.
No full textBACKGROUND: The burden of imported malaria is predominantly in travellers visiting friends and relatives (VFR) in sub-Saharan Africa. The failure of this group to use chemoprophylaxis is recognized as the most important risk factor for the high incidence of disease. Understanding the reasons for failure to follow national recommendations may relate to knowledge, risk perception, cost, and peer pressure. Research into these variables is critical to understand and change practices in this group and this study was designed to explore whether knowledge, risk perception and prophylaxis use differs between travellers' to various destinations and the rest of the UK population. METHODS: Two face-to-face questionnaire surveys were conducted to collect information on demographics, malaria knowledge, source, and quality of pre-travel advice, past travel experience and perceived malaria threat. One was an IPSOS survey of individuals representative of the UK population. The other was a departure lounge survey (Civil Aviation Authority (CAA)) of passengers departing to malarious regions detailing destinations and use of chemoprophylaxis. RESULTS: Around a quarter of the 1,991 UK population surveyed had previously travelled to a malarious area. Five-hundred departing passengers were interviewed, of which 80% travelled for leisure (56% VFR's) and 42% were travelling to West Africa. Malaria knowledge among the UK population (score 58.6) was significantly lower than that of individuals who had previously travelled or were travelling (63.8 and 70.7 respectively). Malaria knowledge was similar in individuals who had and had not sought pre-travel advice and travellers using and not using chemoprophylaxis for their journey. Leisure travellers to Ghana and Nigeria were predominantly VFRs (74%), whilst 66% of travellers to Kenya were tourists. Despite similar high knowledge scores and perceived (>90%) threat of the lethality of malaria in the three groups, chemoprophylaxis use in Nigerians (50%) was substantially lower than in passengers departing to Kenya (78%) and Ghana (82%). More frequent annual return visits were made to Nigeria (72%) than to Ghana (38%) or Kenya (23%). CONCLUSION: Travellers had more malaria knowledge than the non-travelled UK population. Malaria knowledge, perceived threat, travel experience, and quality of pre-travel advice appear unrelated to the use of chemoprophylaxis in passengers. Reducing malaria in VFR travellers will require strategies other than improving malaria knowledge and enhancing malaria risk awareness
CGHpower: exploring sample size calculations for chromosomal copy number experiments
No full textAbstract Background Determining a suitable sample size is an important step in the planning of microarray experiments. Increasing the number of arrays gives more statistical power, but adds to the total cost of the experiment. Several approaches for sample size determination have been developed for expression array studies, but so far none has been proposed for array comparative genomic hybridization (aCGH). Results Here we explore power calculations for aCGH experiments comparing two groups. In a pilot experiment CGHpower estimates the biological diversity between groups and provides a statistical framework for estimating average power as a function of sample size. As the method requires pilot data, it can be used either in the planning stage of larger studies or in estimating the power achieved in past experiments. Conclusions The proposed method relies on certain assumptions. According to our evaluation with public and simulated data sets, they do not always hold true. Violation of the assumptions typically leads to unreliable sample size estimates. Despite its limitations, this method is, at least to our knowledge, the only one currently available for performing sample size calculations in the context of aCGH. Moreover, the implementation of the method provides diagnostic plots that allow critical assessment of the assumptions on which it is based and hence on the feasibility and reliability of the sample size calculations in each case. The CGHpower web application and the program outputs from evaluation data sets can be freely accessed at http://www.cangem.org/cghpower/</p
Diagnostic accuracy of D-dimer test for exclusion of venous thromboembolism: a systematic review
No full textBACKGROUND: The reported diagnostic accuracy of the D-dimer test for exclusion of
deep vein thrombosis (DVT) and pulmonary embolism (PE) varies. It is unknown to
what extent this is due to differences in study design or patient groups, or to
genuine differences between D-dimer assays.
METHODS: Studies evaluating the diagnostic accuracy of the D-dimer test in the
diagnosis of venous thromboembolism were systematically searched for in the
MEDLINE and EMBASE databases up to March 2005. Reference lists of all included
studies and of reviews related to the topic of the present meta-analysis were
manually searched for other additional potentially eligible studies. Two
reviewers independently extracted study characteristics using standardized forms.
RESULTS: In total, 217 D-dimer test evaluations for DVT and 111 for PE were
analyzed. Several study design characteristics were associated with systematic
differences in diagnostic accuracy. After adjustment for these features, the
sensitivities of the D-dimer enzyme-linked immunofluorescence assay (ELFA) (DVT
96%; PE 97%), microplate enzyme-linked immunosorbent assay (ELISA) (DVT 94%; PE
95%), and latex quantitative assay (DVT 93%; PE 95%) were superior to those of
the whole-blood D-dimer assay (DVT 83%; PE 87%), latex semiquantitative assay
(DVT 85%; PE 88%) and latex qualitative assay (DVT 69%; PE 75%). The latex
qualitative and whole-blood D-dimer assays had the highest specificities (DVT
99%, 71%; PE 99%, 69%).
CONCLUSIONS: Compared to other D-dimer assays, the ELFA, microplate ELISA and
latex quantitative assays have higher sensitivity but lower specificity,
resulting in a more confident exclusion of the disease at the expense of more
additional imaging testing. These conclusions are based on the most up-to-date
and extensive systematic review of the topic area, including 184 articles, with
328 D-dimer test evaluations
Sources of bias in diagnostic accuracy studies [Bronnen van bias in onderzoek naar diagnostische accuratesse] [oral]
No full text- Marble slab with a Persian inscription of Jahāngīr dated AH 1027
No full textMarble slab with a Persian inscription of Jahāngīr dated AH 102
A new reading for the Abbasid dinar in the name of caliph Al-Mu tamid Ala Allah (AH 256-279) minted in Al-Ma Suq 271 AH
No full textThe case of a dinar minted ill 271 AH recording the he Caliph
al-Mu'tainid 'ala Allah (256-279 AH), al-Mufawwatj ila Allah (256-278 H),
and an enigmatic mint place is discussed in the paper. The Author attempts to
offer a new reading of the toponym of the mint using literary sources. The love
story between al-Mu'tamid and a Bedouin girl, seems to unveil the identity of
the mysterious mint
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