Home About us Contact
|
Home About us Contact | ||
|
|
||
Substantial Bias (substantial + bias)
Selected AbstractsThe Impact of Uncertainty ShocksECONOMETRICA, Issue 3 2009Nicholas Bloom Uncertainty appears to jump up after major shocks like the Cuban Missile crisis, the assassination of JFK, the OPEC I oil-price shock, and the 9/11 terrorist attacks. This paper offers a structural framework to analyze the impact of these uncertainty shocks. I build a model with a time-varying second moment, which is numerically solved and estimated using firm-level data. The parameterized model is then used to simulate a macro uncertainty shock, which produces a rapid drop and rebound in aggregate output and employment. This occurs because higher uncertainty causes firms to temporarily pause their investment and hiring. Productivity growth also falls because this pause in activity freezes reallocation across units. In the medium term the increased volatility from the shock induces an overshoot in output, employment, and productivity. Thus, uncertainty shocks generate short sharp recessions and recoveries. This simulated impact of an uncertainty shock is compared to vector autoregression estimations on actual data, showing a good match in both magnitude and timing. The paper also jointly estimates labor and capital adjustment costs (both convex and nonconvex). Ignoring capital adjustment costs is shown to lead to substantial bias, while ignoring labor adjustment costs does not. [source] THE COMBINED EFFECT OF DONATION PRICE AND ADMINISTRATIVE INEFFICIENCY ON DONATIONS TO US NONPROFIT ORGANIZATIONSFINANCIAL ACCOUNTABILITY & MANAGEMENT, Issue 1 2009Fred A. Jacobs We examine the effects that two accounting measures of nonprofit organization (NPO) inefficiency, administrative inefficiency and donation price, have on donations to US NPOs using a better-specified model and industry-specific samples. Although numerous studies examine the effect that donation price has on donations (e.g., Marudas and Jacobs, 2006; Marudas, 2004; Khanna and Sandler, 2000; and Tinkelman, 1999), only three studies examine the effect of administrative inefficiency on donations (Tinkelman and Mankaney, 2007; Frumkin and Kim, 2001; and Greenlee and Brown, 1999). However, none of these studies tests donation price and administrative inefficiency in one model and only two test industry-specific samples of NPOs. We find that misspecifying the model by including only one of these two inefficiency measures creates substantial bias and the effect of administrative inefficiency on donations varies substantially across industries. Administrative inefficiency has a significantly negative effect on donations to NPOs in the full sample and the philanthropy sample, but no significant effect on donations to NPOs in the arts, education, health, or human services samples. Furthermore, donation price has a significantly negative effect on donations to NPOs in the full sample and the education, health and human services samples, but not in the arts or philanthropy samples. Results are also reported for the other variables in the model , government support, program service revenue, fundraising and organizational age, wealth and size. [source] Robust estimation and testing of haplotype effects in case-control studies,,GENETIC EPIDEMIOLOGY, Issue 1 2008Andrew S. Allen Abstract Haplotype-based analyses are thought to play a major role in the study of common complex diseases. This has led to the development of a variety of statistical methods for detecting disease-haplotype associations from case-control study data. However, haplotype phase is often uncertain when only genotype data is available. Methods that account for haplotype ambiguity by modeling the distribution of haplotypes can, if this distribution is misspecified, lead to substantial bias in parameter estimates even when complete genotype data is available. Here we study estimators that can be derived from score functions of appropriate likelihoods. We use the efficient score approach to estimation in the presence of nuisance parameters to a derive novel estimators that are robust to the haplotype distribution. We establish key relationships between estimators and study their empirical performance via simulation. Genet. Epidemiol. 2007. Published 2007 Wiley-Liss, Inc. [source] Use and misuse of the IUCN Red List Criteria in projecting climate change impacts on biodiversityGLOBAL CHANGE BIOLOGY, Issue 11 2006H. RESIT AKÇAKAYA Abstract Recent attempts at projecting climate change impacts on biodiversity have used the IUCN Red List Criteria to obtain estimates of extinction rates based on projected range shifts. In these studies, the Criteria are often misapplied, potentially introducing substantial bias and uncertainty. These misapplications include arbitrary changes to temporal and spatial scales; confusion of the spatial variables; and assume a linear relationship between abundance and range area. Using the IUCN Red List Criteria to identify which species are threatened by climate change presents special problems and uncertainties, especially for shorter-lived species. Responses of most species to future climate change are not understood well enough to estimate extinction risks based solely on climate change scenarios and projections of shifts and/or reductions in range areas. One way to further such understanding would be to analyze the interactions among habitat shifts, landscape structure and demography for a number of species, using a combination of models. Evaluating the patterns in the results might allow the development of guidelines for assigning species to threat categories, based on a combination of life history parameters, characteristics of the landscapes in which they live, and projected range changes. [source] Surveying older people from minority ethnic groups: an evaluation of a primary care sampling method for UK African-Caribbean eldersINTERNATIONAL JOURNAL OF METHODS IN PSYCHIATRIC RESEARCH, Issue 4 2002Dr Robert Stewart Abstract There are substantial logistical difficulties in conducting community surveys of minority ethnic group populations. Primary care lists have been identified as an important potential resource but the representativeness of samples derived through this method has received little evaluation. In a community survey of psychiatric morbidity, African-Caribbean people aged 55,75 were identified by practice staff from registration lists for seven primary care teams in south London. The sensitivity of the process was evaluated by contacting a random sample of people whose ethnicity was not known. Participants aged 65,75 (n = 174) were also compared to a similarly aged group sampled through household enumeration (n = 34) with respect to demographic factors, risk factors for vascular disease, depression and cognitive function. For those with correct addresses, the identified group was estimated to include 72% of the potentially eligible population. Only 8% of contacted people were found not to be eligible in terms of ethnicity. Compared to the household enumeration sample, the primary care sample had marginally higher socio-economic status but was similar with respect to all other measured characteristics. Primary care list sampling with staff-assigned ethnicity therefore appeared highly specific, reasonably sensitive, and did not seem to introduce substantial bias for this population. Copyright © 2002 Whurr Publishers Ltd. [source] Impact implantation of a transmitter on Sarpa salpa behaviour: study with a computerized video tracking systemJOURNAL OF FISH BIOLOGY, Issue 2 2005C. Jadot Two transmitter masses (2 and 6% of the fish's mass) were selected to examine the interference of tags with the behaviour of Sarpa salpa using a computerized video tracking system based on digital imaging techniques. The study demonstrated that light transmitters had no effect on the behavioural variables studied, and a substantial bias in behaviour is introduced if heavier (6%) tags are used. [source] Joint generalized estimating equations for multivariate longitudinal binary outcomes with missing data: an application to acquired immune deficiency syndrome dataJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES A (STATISTICS IN SOCIETY), Issue 1 2009Stuart R. Lipsitz Summary., In a large, prospective longitudinal study designed to monitor cardiac abnormalities in children born to women who are infected with the human immunodeficiency virus, instead of a single outcome variable, there are multiple binary outcomes (e.g. abnormal heart rate, abnormal blood pressure and abnormal heart wall thickness) considered as joint measures of heart function over time. In the presence of missing responses at some time points, longitudinal marginal models for these multiple outcomes can be estimated by using generalized estimating equations (GEEs), and consistent estimates can be obtained under the assumption of a missingness completely at random mechanism. When the missing data mechanism is missingness at random, i.e. the probability of missing a particular outcome at a time point depends on observed values of that outcome and the remaining outcomes at other time points, we propose joint estimation of the marginal models by using a single modified GEE based on an EM-type algorithm. The method proposed is motivated by the longitudinal study of cardiac abnormalities in children who were born to women infected with the human immunodeficiency virus, and analyses of these data are presented to illustrate the application of the method. Further, in an asymptotic study of bias, we show that, under a missingness at random mechanism in which missingness depends on all observed outcome variables, our joint estimation via the modified GEE produces almost unbiased estimates, provided that the correlation model has been correctly specified, whereas estimates from standard GEEs can lead to substantial bias. [source] A parallel analysis of individual and ecological data on residential radon and lung cancer in south-west EnglandJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES A (STATISTICS IN SOCIETY), Issue 1 2001Sarah Darby Parallel individual and ecological analyses of data on residential radon have been performed using information on cases of lung cancer and population controls from a recent study in south-west England. For the individual analysis the overall results indicated that the relative risk of lung cancer at 100 Bq m,3 compared with at 0 Bq m,3 was 1.12 (95% confidence interval (0.99, 1.27)) after adjusting for age, sex, smoking, county of residence and social class. In the ecological analysis substantial bias in the estimated effect of radon was present for one of the two counties involved unless an additional variable, urban,rural status, was included in the model, although this variable was not an important confounder in the individual level analysis. Most of the methods that have been recommended for overcoming the limitations of ecological studies would not in practice have proved useful in identifying this variable as an appreciable source of bias. [source] Comparison of different near-infrared spectroscopic cerebral oxygenation indices with central venous and jugular venous oxygenation saturation in childrenPEDIATRIC ANESTHESIA, Issue 2 2008NICOLE NAGDYMAN Summary Background:, We compared two different near-infrared spectrophotometers: cerebral tissue oxygenation index (TOI) measured by NIRO 200 and regional cerebral oxygenation index (rSO2) measured by INVOS 5100 with venous oxygen saturation in the jugular bulb (SjO2) and central SvO2 from the superior caval vein (SVC) during elective cardiac catheterization in children. Methods:, A prospective observational clinical study in 31 children with congenital heart defects in a catheterization laboratory was undertaken. TOI was compared with SjO2 in the left jugular bulb and with SvO2. rSO2 was compared with SjO2 from the right jugular bulb and SvO2. Linear regression analysis and Pearson's correlation coefficient were calculated and Bland,Altman analyses were performed. Results:, Cerebral TOI and SjO2 were significantly correlated (r = 0.56, P < 0.0001), as well as TOI and SvO2 with r = 0.74 (P < 0.0001). Bland,Altman plots showed a mean bias of ,4.3% with limits of agreement of 15.7% and ,24.3% for TOI and SjO2 and a mean bias of ,4.9% with limits of agreement of 10.3% and ,20.1% for TOI and SvO2. Cerebral rSO2 and SjO2 showed a significant correlation (r = 0.83, P < 0.0001) and rSO2 and SvO2 showed excellent correlation with r = 0.93 (P < 0.0001). Bland,Altman plots showed a mean bias of ,5.2% with limits of agreement of between 8.4% and ,18.8% for rSO2 and SjO2 and a mean bias of 5.6% with limits of agreement of 13.4% and ,2.2% for rSO2 and SvO2. Conclusions:, Both near-infrared spectroscopy devices demonstrate a significant correlation with SjO2 and SvO2 values; nevertheless both devices demonstrate a substantial bias of the measurements to both SjO2 and SvO2. [source] Right movies on the right seat: Laterality and seat choiceAPPLIED COGNITIVE PSYCHOLOGY, Issue 1 2010Matia Okubo Various forms of lateral preferences are found in human behaviour. Conducting two experiments, we investigated the lateral preference for seat choice exhibited by people at the movie theatre. The right-handed participants (N,=,269) tended to choose seats to the right of the screen when they were positively motivated to see the movie. This rightward bias disappeared when they were negatively motivated. In addition, the non-right-handed participants (N,=,105) did not show any substantial bias in their seat choice. It is well known that visual and emotional information is better processed in the right hemisphere. Considering the visual and emotional nature of movie experiences, the rightward seating bias among right-handers appears to be determined by their motivation to effectively utilize their right-hemisphere functions. Copyright © 2009 John Wiley & Sons, Ltd. [source] | ||||||||||||||||