Overconfidence of Professionals and Lay Men: Individual Differences Within and Between Tasks?

Overconfidence can manifest itself in various forms. For example, people think that their knowledge is more precise than it really is (miscalibration) and they believe that their abilities are above average (better than average effect). The questions whether judgment biases are related or whether stable individual differences in the degree of overconfidence exist, have long been unexplored. In this paper, we present two studies that analyze whether professional traders or investment bankers who work for international banks are prone to judgment biases to the same degree as a population of lay men. We examine whether there are robust individual differences in the degree of overconfidence within various tasks. Furthermore, we analyze whether the degree of judgment biases is correlated across tasks. Based on the answers of 123 professionals, we find that expert judgment is biased. In most tasks, their degrees of overconfidence are significantly higher than the respective scores of a student control group. In line with the literature, we find stable individual differences within tasks (e.g. in the degree of miscalibration). However, we find that correlations across distinct tasks are sometimes insignificant or even negative. We conclude that some manifestations of overconfidence, that are often argued to be related, are actually unrelated.

Downbeat nystagmus: aetiology and comorbidity in 117 patients

Objectives: Downbeat nystagmus (DBN) is the most common form of acquired involuntary ocular oscillation overriding fixation. According to previous studies, the cause of DBN is unsolved in up to 44% of cases. We reviewed 117 patients to establish whether analysis of a large collective and improved diagnostic means would reduce the number of cases with ``idiopathic DBN'' and thus change the aetiological spectrum.Methods: The medical records of all patients diagnosed with DBN in our Neurological Dizziness Unit between 1992 and 2006 were reviewed. In the final analysis, only those with documented cranial MRI were included. Their workup comprised a detailed history, standardised neurological, neuro-otological and neuro-ophthalmological examination, and further laboratory tests.Results: In 62% (n = 72) of patients the aetiology was identified (``secondary DBN''), the most frequent causes being cerebellar degeneration (n = 23) and cerebellar ischaemia (n = 10). In 38% (n = 45), no cause was found (``idiopathic DBN''). A major finding was the high comorbidity of both idiopathic and secondary DBN with bilateral vestibulopathy (36%) and the association with polyneuropathy and cerebellar ataxia even without cerebellar pathology on MRI.Conclusions: Idiopathic DBN remains common despite improved diagnostic techniques. Our findings allow the classification of ``idiopathic DBN'' into three subgroups: ``pure'' DBN (n = 17); ``cerebellar'' DBN (ie, DBN plus further cerebellar signs in the absence of cerebellar pathology on MRI; n = 6); and a ``syndromatic'' form of DBN associated with at least two of the following: bilateral vestibulopathy, cerebellar signs and peripheral neuropathy (n = 16). The latter may be caused by multisystem neurodegeneration

Overconfidence of professionals and lay men : individual differences within and between tasks?

Overconfidence can manifest itself in various forms. For example, people think that their knowledge is more precise than it really is (miscalibration) and they believe that their abilities are above average (better than average effect). The questions whether judgment biases are related or whether stable individual differences in the degree of overconfidence exist, have long been unexplored. In this paper, we present two studies that analyze whether professional traders or investment bankers who work for international banks are prone to judgment biases to the same degree as a population of lay men. We examine whether there are robust individual differences in the degree of overconfidence within various tasks. Furthermore, we analyze whether the degree of judgment biases is correlated across tasks. Based on the answers of 123 professionals, we find that expert judgment is biased. In most tasks, their degrees of overconfidence are significantly higher than the respective scores of a student control group. In line with the literature, we find stable individual differences within tasks (e.g. in the degree of miscalibration). However, we find that correlations across distinct tasks are sometimes insignificant or even negative. We conclude that some manifestations of overconfidence, that are often argued to be related, are actually unrelated

Flupenthixol in relapse prevention in schizophrenics with comorbid alcoholism: Results from an open clinical study

Substance use, especially alcoholism, has been recognized as a significant problem in schizophrenic patients, though only a few studies on the effects of pharmacotherapy in these patients have been conducted so far. The thioxanthene neuroleptic flupenthixol, which can be given intramuscularly (i.m.) for improving compliance, has been studied as a possible anti-craving drug both in animal models of alcoholism and some clinical studies. Pilot studies suggest that comorbid schizophrenics with substance use may benefit from treatment with flupenthixol. Efficacy of flupenthixol (10-60 mg i.m.) in reducing alcohol consumption of dual diagnosis patients was studied in an open 6-month clinical trial in 27 schizophrenics with comorbid alcoholism. Twenty-one patients entered the intention-to-treat analysis. Fourteen subjects were completers, 13 dropped out. Six patients completely abstained from alcohol during treatment. Alcohol consumption was significantly reduced compared to baseline (4 weeks before treatment as measured by timeline follow-back interview). In general, while patients showed a marked improvement concerning alcohol consumption, only a slight improvement in psychopathology was recorded. Overall tolerability was good. These data indicate a probable beneficial effect of flupenthixol in schizophrenic patients with comorbid alcoholism. Although the efficacy of flupenthixol as an anti-craving drug in dual diagnosis patients has to be explored in further studies, the drug may be considered a promising medication for these patients. Copyright (C) 2003 S. Karger AG, Basel

Extrinsic curvature in two-dimensional causal dynamical triangulation

Causal dynamical triangulation (CDT) is a nonperturbative quantization of general relativity. Hořava-Lifshitz gravity, on the other hand, modifies general relativity to allow for perturbative quantization. Past work has given rise to the speculation that Hořava-Lifshitz gravity might correspond to the continuum limit of CDT. In this paper we add another piece to this puzzle by applying the CDT quantization prescription directly to Hořava-Lifshitz gravity in two dimensions. We derive the continuum Hamiltonian, and we show that it matches exactly the Hamiltonian derived from canonically quantizing the Hořava-Lifshitz action. Unlike the standard CDT case, here the introduction of a foliated lattice does not impose further restriction on the configuration space and, as a result, lattice quantization does not leave any imprint on continuum physics as expected

Scale Dependence of Overconfidence in Stock Market Volatility Forecasts

In this study, we analyze whether volatility forecasts (judgmental confidence intervals) are influenced by the specific elicitation mode (i.e. whether forecasters have to state future price levels or directly future returns as upper and lower bounds). We present questionnaire responses of about 250 students from two German universities. Participants were asked to state median forecasts as well as confidence intervals for seven stock market time series. Using a between subject design, one half of the subjects was asked to state future price levels, the other group was directly asked for returns. Consistent with prior research we find that subjects underestimate the volatility of stock returns, indicating overconfidence. As a new insight, we find that the strength of the overconfidence effect in stock market forecasts is highly significantly affected by the fact whether subjects provide price or return forecasts. Volatility estimates are lower (and the overconfidence bias is thus stronger) when subjects are asked for returns compared to price forecasts

Weighting procedures to counter unit nonresponse bias of estimators for sample surveys

Das Hauptthema der vorliegenden Arbeit sind Verzerrungen von Schätzern aus Stichprobenerhebungen mit freiwilliger Teilnahme, die wegen Antwortausfällen auftreten können. Antwortausfälle aufgrund von nicht an der Erhebung teilnehmenden Erhebungseinheiten führen zu verzerrten Schätzern, wenn der Ausfall nicht komplett zufällig stattfindet. Verschiedene Gewichtungsmethoden können verwendet werden, um diese Verzerrung zu kompensieren. Dazu zählen beispielsweise die Verwendung der Inversen der geschätzten Antwortwahrscheinlichkeiten oder Kalibrierung an externe Randverteilungen. Um mögliche Verzerrungen aufgrund von Antwortausfällen zu untersuchen, wurden Simulationen durchgeführt, die einen Vergleich der verschiedenen Schätzer und der verwendeten Gewichtungsmethoden, die vermutlich Verzerrungen entgegenwirken, erlauben. Die Datengrundlage der Simulationen bildet die Erhebung EU-SILC (European Union Statistics on Income and Living Conditions) in Österreich. EU-SILC ist eine Erhebung mit freiwilliger Teilnahme basierend auf einer Wahrscheinlichkeitsstichprobe privater Haushalte in Österreich und einem rotierenden Paneldesign. Die wichtigste Untersuchungsvariable für die vorliegende Arbeit ist ein Bestandteil des gesamten Haushaltseinkommens (Einkommen aus unselbständiger Tätigkeit und Alterspensionen). Die Summe dieser Variable über alle Haushalte in der Population wurde als zu schätzender Parameter gewählt. Der Antwortprozess wurde für die gezogene Stichprobe der Erstbefragung EU-SILC 2010 simuliert und der Erwartungswert der verschiedenen Schätzungen, basierend auf den teilnehmenden Haushalten, wurde mit der designgewichteten Schätzung der gezogenen Stichprobe verglichen. Die Ergebnisse zeigen, dass ohne eine Anpassung der Gewichte an den Antwortausfall der Schätzer für den Wert in der Grundgesamtheit verzerrt ist. Gewichtungsmethoden, die Hilfsvariablen zur Kompensation des Antwortausfalls verwenden, können Verzerrungen verkleinern. Kalibrierungen an externe Randverteilungen resultierten schließlich in Schätzern mit der höchsten Präzision, da sie nicht nur vergleichsweise kleine Verzerrungen aufweisen, sondern auch zu einer verringerten Varianz führen.The main topic of the present thesis is bias of estimators from sample surveys with voluntary participation that may occur because of unit nonresponse. If not all units selected in the sample take part in the survey, this may lead to bias in estimators if the event of unit nonresponse does not happen completely at random. Weighting methods can be used to compensate for this bias. Therefore, suitable methods like using the inverse of estimated response probabilities to adjust for unit nonresponse or calibration to external marginal distributions are presented. In order to investigate potential bias due to unit nonresponse, simulations were carried out to make a comparison of different estimators applying various weighting methods that presumably counter bias. The data for these simulations were taken from the survey EU-SILC (European Union Statistics on Income and Living Conditions) in Austria. EU-SILC is a probability sample survey of private households in Austria that employs a rotating panel design. Participation in the survey is voluntary. The survey variable of interest in this thesis is a component of the household income (income from employment and old-age benefits). The sum of this variable over all households in the population is the parameter that was chosen to be estimated from the respondents of the selected sample. The response process was simulated for the selected sample of the first wave of EU-SILC 2010 and the expectation of different estimators calculated from the simulated response sets was compared to the design-weighted estimate of the selected sample. Results show that no adjustment for unit nonresponse leads to a biased estimator. Weighting methods that use auxiliary information to adjust for unit nonresponse bias can reduce this bias. The most precise estimators result from calibration, because this method reduces bias and also facilitates a reduction of variance