The Effects of feedback on judgmental interval predictions

Cataloged from PDF version of article.The majority of studies of probability judgment have found that judgments tend to be overconfident and that the degree of overconfidence is greater the more difficult the task. Further, these effects have been resistant to attempts to ‘debias’ via feedback. We propose that under favourable conditions, provision of appropriate feedback should lead to significant improvements in calibration, and the current study aims to demonstrate this effect. To this end, participants first specified ranges within which the true values of time series would fall with a given probability. After receiving feedback, forecasters constructed intervals for new series, changing their probability values if desired. The series varied systematically in terms of their characteristics including amount of noise, presentation scale, and existence of trend. Results show that forecasts were initially overconfident but improved significantly after feedback. Further, this improvement was not simply due to ‘hedging’, i.e. shifting to very high probability estimates and extremely wide intervals; rather, it seems that calibration improvement was chiefly obtained by forecasters learning to evaluate the extent of the noise in the series. D 2003 International Institute of Forecasters. Published by Elsevier B.V. All rights reserved

Nitrogen Mineralization from Root Residues of Subterranean Clover and Lucerne

To understand why crops grown in the first or second year after lucerne (Medicago sativa L.) yielded less than crops grown after subterranean clover (Trifolium subterraneum L.) despite greater nitrogen (N) fixation by the lucerne, we studied the N mineralization patterns of their root residues in soil incubation assays. Fine roots of both species produced more mineral N than the control soil with no root residues. In contrast, coarse roots mineralized less N than the control soil. These differences in N mineralization were not explained by the physical size and therefore surface area differences between fine and coarse roots. Rather, the differences in N mineralization were explained by differences in the carbon to nitrogen ratio (C:N) of fine and coarse roots. Fine roots of both species had a C:N of about 11, while the C:N of coarse roots ranged from 28 to 37. Empirical evidence suggests that a mineralization / immobilization threshold occurs at a C:N of 20 to 30, and these results are in accordance with this interpretation. However, subterranean clover had mainly fine roots giving a weighted average C:N of 19 for the whole root system, while lucerne had mainly coarse roots giving an average C:N of 26, suggesting that root residues of subterranean clover result in a net mineralization of N while lucerne roots cause a net immobilization of N

Mitral Annular and Coronary Artery Calcification Are Associated with Mortality in HIV-Infected Individuals.

BackgroundHIV infection increases cardiovascular risk. Coronary artery calcification (CAC) and mitral annular calcification (MAC) identify patients at risk for cardiovascular disease (CVD). The purpose of this study was to examine the association between MAC, CAC and mortality in HIV-infected individuals.Methods and resultsWe studied 152 asymptomatic HIV-infected individuals with transthoracic echocardiography (TTE) and computed tomography (CT). MAC was identified on TTE using standardized criteria. Presence of CAC, CAC score and CAC percentiles were determined using the modified Agatston criteria. Mortality data was obtained from the Social Security and National Death Indices (SSDI/NDI). The median age was 49 years; 87% were male. The median duration of HIV was 16 years; 84% took antiretroviral therapy; 64% had an undetectable viral load. CVD risk factors included hypertension (35%), smoking (62%) and dyslipidemia (35%). Twenty-five percent of individuals had MAC, and 42% had CAC. Over a median follow-up of 8 years, 11 subjects died. Subjects with CAC had significantly higher mortality compared to those with MAC only or no MAC. The Harrell's C-statistic of CAC was 0.66 and increased to 0.75 when MAC was added (p = 0.05). MAC, prior CVD, age and HIV viral load were independently associated with higher age- and gender-adjusted CAC percentiles in an adjusted model (p < 0.05 for all).ConclusionIn HIV patients, the presence of MAC, traditional risk factors and HIV viral load were independently associated with CAC. Presence of CAC and MAC may be useful in identifying HIV-infected individuals at higher risk for death

Provider-user differences in perceived usefulness of forecasting formats

This paper aims to examine potential differences in perceived usefulness of various forecasting formats from the perspectives of providers and users of predictions. Experimental procedure consists of asking participants to assume the role of forecast providers and to construct forecasts using different formats, followed by requesting usefulness ratings for these formats (Phase 1). Usefulness of the formats are rated again in hindsight after receiving individualized performance feedback (Phase 2). In the ensuing role switch exercise, given new series and external predictions, participants are required to assign usefulness ratings as forecast users (Phase 3). In the last phase, participants are given performance feedback and asked to rate the usefulness in hindsight as users of predictions (Phase 4). Results reveal that regardless of the forecasting role, 95% prediction intervals are considered to be the most useful format, followed by directional predictions, 50% interval forecasts, and lastly, point forecasts. Finally, for all formats and for both roles, usefulness in hindsight is found to be lower than usefulness prior to performance feedback presentation. © 2003 Elsevier Ltd. All rights reserved

Carotid Intima-Media Thickness Progression in HIV-Infected Adults Occurs Preferentially at the Carotid Bifurcation and Is Predicted by Inflammation.

BackgroundShear stress gradients and inflammation have been causally associated with atherosclerosis development in carotid bifurcation regions. The mechanism underlying higher levels of carotid intima-media thickness observed among HIV-infected individuals remains unknown.Methods and resultsWe measured carotid intima-media thickness progression and development of plaque in the common carotid, bifurcation region, and internal carotid artery in 300 HIV-infected persons and 47 controls. The median duration of follow-up was 2.4 years. When all segments were included, the rate of intima-media thickness progression was greater in HIV-infected subjects compared with controls after adjustment for traditional risk factors (0.055 vs. 0.024 mm/year, P=0.016). Rate of progression was also greater in the bifurcation region (0.067 vs. 0.025 mm/year, P=0.042) whereas differences were smaller in the common and internal regions. HIV-infected individuals had a greater incidence of plaque compared with controls in the internal (23% vs. 6.4%, P=0.0037) and bifurcation regions (34% vs. 17%, P=0.014). Among HIV-infected individuals, the rate of progression in the bifurcation region was more rapid compared with the common carotid, internal, or mean intima-media thickness; in contrast, progression rates among controls were similar at all sites. Baseline hsCRP was elevated in HIV-infected persons and was a predictor of progression in the bifurcation region.ConclusionsAtherosclerosis progresses preferentially in the carotid bifurcation region in HIV-infected individuals. hsCRP, a marker of inflammation, is elevated in HIV and is associated with progression in the bifurcation region. These data are consistent with a model in which the interplay between hemodynamic shear stresses and HIV-associated inflammation contribute to accelerated atherosclerosis. (J Am Heart Assoc. 2012;1:jah3-e000422 doi: 10.1161/JAHA.111.000422.)Clinical trial registrationURL: http://clinicaltrials.gov. Unique identifier: NCT01519141

Publisher Correction: Bridging the gap between measurements and modelling: a cardiovascular functional avatar.

An amendment to this paper has been published and can be accessed via a link at the top of the paper