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Slight Bias (slight + bias)
Selected AbstractsHBM functional imaging analysis contest data analysis in wavelet spaceHUMAN BRAIN MAPPING, Issue 5 2006John A.D. Aston Abstract An analysis of the Functional Imaging Analysis Contest (FIAC) data is presented using spatial wavelet processing. This technique allows the image to be filtered adaptively according to the data itself, rather than relying on a predetermined filter. This adaptive filtering leads to better estimation of the parameters and contrasts in terms of mean squared error. It will be shown that by introducing a slight bias into the estimation, a large reduction in the variance can be achieved, leading to better overall mean squared error estimates. As no single filter needs to be preselected, results containing many scales of information can be found. In the FIAC data, it is shown that both small-scale and large-scale (smoother, more dispersed) effects occur. The combination of small- and large-scale effects detected in the FIAC data would be easy to miss using conventional single filter analysis. Hum Brain Mapp, 2006. © 2006 Wiley-Liss, Inc. [source] Measurement of HbA1c from stored whole blood samples in the Atherosclerosis Risk in Communities studyJOURNAL OF DIABETES, Issue 2 2010Elizabeth SELVIN Abstract Background:, The aims of the present study were to demonstrate the reliability of HbA1c measurements during two time periods and to compare these measurements with HbA1c distribution in the general US population. Methods:, HbA1c was measured in 14 069 whole blood samples in the Atherosclerosis Risk in Communities (ARIC) study using different HPLC instruments across two time periods, namely 2003,2004 and 2007,2008. At the time of measurement, samples had been in storage at ,70°C for up to 18 years. To assess differences in values, HbA1c measurements were repeated in 383 samples at both periods. Indirect comparisons were made by comparing our measurements against those from a nationally representative study. Results:, The coefficients of variation for quality control samples were 1.8% (n = 89) in 2003,2004 and 1.4% (n = 259) in 2007,2008. The correlation between measurements at the two time points was high (r = 0.99), but with a slight bias: 0.29% points higher in 2007,2008 vs 2003,2004 (n = 383; P < 0.0001). The comparison yielded the following Deming regression equation: y(2007,2008) = 0.073 + 1.034x(2003,2004). After alignment using this equation, the distribution of HbA1c in the ARIC study was similar to that in the national study using fresh samples. Conclusions:, Measurements of HbA1c from samples stored for up to 18 years are highly reliable when using state-of-the-art HPLC instruments, but with some bias introduced over time. The HbA1c data now available in the ARIC study should be invaluable for investigations into the clinical utility of HbA1c as a diagnostic test for diabetes. [source] Caenorhabditis elegans PI3K mutants reveal novel genes underlying exceptional stress resistance and lifespanAGING CELL, Issue 6 2009Srinivas Ayyadevara Summary Two age-1 nonsense mutants, truncating the class-I phosphatidylinositol 3-kinase catalytic subunit (PI3KCS) before its kinase domain, confer extraordinary longevity and stress-resistance to Caenorhabditis elegans. These traits, unique to second-generation homozygotes, are blunted at the first generation and are largely reversed by additional mutations to DAF-16/FOXO, a transcription factor downstream of AGE-1 in insulin-like signaling. The strong age-1 alleles (mg44, m333) were compared with the weaker hx546 allele on expression microarrays, testing four independent cohorts of each allele. Among 276 genes with significantly differential expression, 92% showed fewer transcripts in adults carrying strong age-1 alleles rather than hx546. This proportion is significantly greater than the slight bias observed when contrasting age-1 alleles to wild-type worms. Thus, transcriptional changes peculiar to nonsense alleles primarily involve either gene silencing or failure of transcriptional activation. A subset of genes responding preferentially to age-1- nonsense alleles was reassessed by real-time polymerase chain reaction, in worms bearing strong or weak age-1 alleles; nearly all of these were significantly more responsive to the age-1(mg44) allele than to age-1(hx546). Additional mutation of daf-16 reverted the majority of altered mg44 -F2 expression levels to approximately wild-type values, although a substantial number of genes remained significantly distinct from wild-type, implying that age-1(mg44) modulates transcription through both DAF-16/FOXO-dependent and independent channels. When age-1 -inhibited genes were targeted by RNA interference (RNAi) in wild-type or age-1(hx546) adults, most conferred significant oxidative-stress protection. RNAi constructs targeting two of those genes were shown previously to extend life, and RNAi's targeting five novel genes were found here to increase lifespan. PI3K - null mutants may thus implicate novel mechanisms of life extension. [source] Complementary Log,Log Regression for the Estimation of Covariate-Adjusted Prevalence Ratios in the Analysis of Data from Cross-Sectional StudiesBIOMETRICAL JOURNAL, Issue 3 2009Alan D. Penman Abstract We assessed complementary log,log (CLL) regression as an alternative statistical model for estimating multivariable-adjusted prevalence ratios (PR) and their confidence intervals. Using the delta method, we derived an expression for approximating the variance of the PR estimated using CLL regression. Then, using simulated data, we examined the performance of CLL regression in terms of the accuracy of the PR estimates, the width of the confidence intervals, and the empirical coverage probability, and compared it with results obtained from log,binomial regression and stratified Mantel,Haenszel analysis. Within the range of values of our simulated data, CLL regression performed well, with only slight bias of point estimates of the PR and good confidence interval coverage. In addition, and importantly, the computational algorithm did not have the convergence problems occasionally exhibited by log,binomial regression. The technique is easy to implement in SAS (SAS Institute, Cary, NC), and it does not have the theoretical and practical issues associated with competing approaches. CLL regression is an alternative method of binomial regression that warrants further assessment. [source] Sensitivity to the acceleration of looming stimuliCLINICAL & EXPERIMENTAL OPHTHALMOLOGY, Issue 3 2003James Trewhella BSc(Hons) Abstract The aim of this study was to determine if observers could discriminate between looming stimuli simulating targets approaching the observers at either constant or non-constant speeds. Discrimination between accelerating and constant-speed approaches improved after 70,90 trials for accelerations >2 m/s2. For lower accelerations the ability to discriminate was poor regardless of the trial number. Following the learning phase, observers were able to identify accelerating targets from constant-speed approaches fairly consistently at performance levels of 70,75% for accelerations as low as 4 m/s2 and at 80,96% for accelerations of 6,14 m/s2. Observers' accuracy in identifying decelerating from constant-speed targets did not increase as a function of increasing deceleration. In fact, observers had a slight bias to select the constant-speed stimulus as being the decelerating stimulus. In summary, the sensitivity to acceleration for simulated motion in depth is poor, but increases as acceleration increases and sensitivity to acceleration is far greater than for deceleration. [source] | |||||||||||||