Testing for rational bubbles in a coexplosive vector autoregression

Summary Asset bubbles can be described through the rational bubble solution of the standard stock price model linking stock prices and dividends. We show how the hypothesis of a rational bubble can be tested in the context of a bivariate coexplosive vector autoregression. The methodology is illustrated using US stock prices and dividends for the period 1974–2000.     

HCV实验室检测方法与临床应用

HCV感染的实验室检测方法包括血清免疫检测和核酸检测。本文对各种方法和不同项目的特点、意义、应用范围及相互关系进行介绍,为临床医生在丙型肝炎诊治时对实验室项目的选择以及结果的解释提供帮助。     

A simple decision analytic solution to the comparison of two binary diagnostic tests

One of the most basic biostatistical problems is the comparison of two binary diagnostic tests. Commonly, one test will have greater sensitivity, and the other greater specificity. In this case, the choice of the optimal test generally requires a qualitative judgment as to whether gains in sensitivity are offset by losses in specificity. Here, we propose a simple decision analytic solution in which sensitivity and specificity are weighted by an intuitive parameter, the threshold probability of disease at which a patient will opt for treatment. This gives a net benefit that can be used to determine which of two diagnostic tests will give better clinical results at a given threshold probability and whether either is superior to the strategy of assuming that all or no patients have disease. We derive a simple formula for the relative diagnostic value, which is the difference in sensitivities of two tests divided by the difference in the specificities. We show that multiplying relative diagnostic value by the odds at the prevalence gives the odds of the threshold probability below which the more sensitive test is preferable and above which the more specific test should be chosen. The methodology is easily extended to incorporate combinations of tests and the risk or side effects of a test. Copyright © 2012 John Wiley & Sons, Ltd.     

Comparing diagnostic tests: trials in people with discordant test results

Diagnostic tests are traditionally compared for accuracy against a gold standard but can also be compared prospectively in a trial. A conventional trial comparing two tests would randomize each participant to a testing strategy, but a more efficient alternative is to give both tests to all participants and follow up those with discordant results. Participants could be randomized before or after testing. The statistical analysis of such a trial has not previously been described. We investigated two estimates of the risk difference for a binary outcome: one based on analysing outcomes as if from a conventional trial and one combining estimates of different parameters in the manner of a decision analysis. We show that the trial estimate and decision analysis estimate are both unbiased and derive approximate formulae for their standard errors. By using the decision analysis estimate (but not the trial estimate), the same precision can be achieved by randomizing before testing as by randomizing after. To avoid destroying equipoise, and to allow consenting and randomizing to be carried out at the same visit, we recommend randomizing before testing. Giving both tests to all participants means fewer need to be recruited: in one example from the literature, the proposed design was nearly four times more efficient in this sense than a conventional trial design. Copyright © 2012 John Wiley & Sons, Ltd.     

Benefits of Swimming in Asthma: Effect of a Session of Swimming Lessons on Symptoms and PFTs with Review of the Literature

A study involving eight children with moderate persistent asthma was undertaken to determine whether standard swimming lessons improved symptoms and pulmonary function tests (PFTs) in asthmatic children. Five children ages 7–12 years old with moderate persistent asthma were randomized to a swimming lesson group (5- to 6-week session) and three to a control group. Both groups completed pre- and poststudy period PFTs and symptom questionnaires. Swimming lessons did not produce a significant change in asthma symptoms or PFTs. Review of previous literature found that swimming has been shown to have definite benefits in improving cardiorespiratory fitness in asthmatic children. Swimming has been shown to be less asthmogenic than other forms of exercise. Some studies have also shown improvement in asthma symptoms in children participating in exercise programs.     

Effect of Azelastine Nasal Spray on Histamine-and Allergen-Induced Skin Wheal Response in Patients with Allergic Rhinitis

Effect of azelastine nasal spray on histamine-and allergen-induced skin test response in patients suffering with allergic rhinitis was evaluated. Baseline cutaneous response to histamine and 18 common allergen extracts were recorded by skin prick tests on 10 patients. The patients were then advised to take azelastine nasal spray (1 spray per nostril, twice daily; 0.28 mg/dose). This pediatric dose is reported to be effective also in adults (age ≥ 12 years) with improved tolerability as compared with usually recommended adult dose of 2 sprays per nostril twice daily. Skin tests were repeated 2 and 6 hours after single dose, as well as after 6 days of continuous treatment. We did not find any significant difference in skin wheal response with single dose and 6 days' treatment of azelastine nasal spray (p > 0.05). It is concluded that diagnostic allergen skin tests may be performed on patients undergoing azelastine nasal spray treatment (0.28 mg/dose, twice a day) during their symptomatic period.     

Intestinal Metaplasia,High-Grade Epithelial Dysplasia and Gastric Cancer

Abstract

Objective. In 1990, Lavelle and Kanagaratnam introduced Usefulness Index (UI) test for assessment of usefulness of clinical observations. Although, nonspecific abdominal pain (NSAP) is the most common diagnosis among secondary care patients with acute abdominal pain, the efficiency of UI test is rarely considered in NSAP. Methods. In an extension of the World Organisation of Gastro-Enterology Research Committee (OMGE) acute abdominal pain study, 1333 patients presenting with acute abdominal pain were included in the study. The clinical signs (n = 14) and tests (n = 3) in each patient were recorded in detail, using a predefined structured data collection sheet, and the collected data were compared with the final diagnoses of the patients. Results. The most significant clinical tests and signs of NSAP in univariate analysis were (UI = Usefulness Index and RR = risk ratio): rigidity (UI = 0.36, RR = 32.2), rebound (UI = 0.33, RR = 6.3), guarding (UI = 0.25, RR = 4.9), Murphy's positive (UI = 0.13, 8.9), bowel sounds (UI = 0.12, RR = 3.3), and renal tenderness (UI = 0.12, RR = 2.2). The sensitivity of the doctors' initial decision in detecting NSAP was 0.70 with a specificity of 0.83 and with the UI = 0.37 and RR = 11.4. Conclusion. The patients with negative test results in rigidity, rebound, guarding, Murphy's, and bowel sounds tended to be at risk for NSAP and in these patients the UI test could be an aid for clinician to differentiate NSAP from other causes of acute abdominal pain.     

Absence of Correlation Between the Spontaneously Hypertensive Rat's Exaggerated Preference for Sweet and Alcohol Drinking Solutions

We tested the hypothesis that the exaggerated preference of the spontaneously hypertensive rat of the Okamoto strain (SHR) for alcohol-containing drinking solutions is due to its exaggerated preference for the purported sweet subtaste of alcohol. To do, this we examined in SHR (and Brown Norway (BN) controls) whether preferences for alcohol and glucose-drinking solutions were correlated. No significant correlation was found between alcohol and glucose preference in either the SHR or BN. We conclude therefore that the exaggerated alcohol preference of the SHR is not due to an exaggerated preference for the purported sweet subtaste of alcohol.     

Kidney Function in Heart Failure

Objective. The purpose of this investigation was to improve a rankit ordinal model for evaluating and validating dichotomized tests in a prospective Nordic project. Material and methods. The model is based on the assumption that the S‐shaped curve of fractions of positive for increasing concentrations can be de‐convoluted to a histogram and thereby used to calculate the parameters for a ln‐Gaussian distribution. In a Nordic survey, four urine samples with known concentrations of hCG (human chorionic gonadotrophin) and nitrites were distributed to more than 2500 practitioners' offices. Results. The results are presented as parameters (geometric mean and CV) for the components urine‐hCG and urine‐nitrites, together with fractions of positive for clinical critical values (5 and 40?IU/L for hCG), for which fractions should be below 0.01 and above 0.99, respectively, and 7?µmol/L for nitrites. Furthermore, the concentration intervals of varying fractions of positive from 0.01 to 0.99 are estimated as grey zones. The parameters and grey zones for different kits are compared. No urine‐hCG kit fulfilled the low clinical criterion, whereas all fulfilled the high criterion. Seven of the eight nitrites kits had fractions of positive above 0.9 for the company confirmation limit, but varying fractions for the clinically important limit of 7?µmol/L (fractions from 0.06 to 0.83). Conclusions. The present model makes it easy to estimate parameters for the kits, and also to estimate the fractions of measured positives for specified concentrations. It is thus suited for external quality assessment as well as for manufacturers' method validation.