scholarly journals Comparison of Two Measures of Missing Cofactor in Cofactor-Dependent Enzymes: Proportion Versus Relative Increase

2012 ◽  
Vol 5 (1) ◽  
pp. 16-21 ◽  
Author(s):  
Tomas Hansson
Keyword(s):  
Statistical Power ◽  
Relative Increase ◽  
Statistical Properties ◽  
Sensitive Measure ◽  
Power Difference ◽  
Two Measures

The degree of missing cofactor in a cofactor-dependent enzyme is widely used as a biomarker of cofactor defi-ciency. The degree of missing cofactor can be expressed either as the proportion of enzyme without cofactor, or as the rel-ative increase in enzyme with cofactor after addition of excess cofactor to the sample. Especially for enzymes with thia-mine pyrophosphate (TPP) as a cofactor, the relative increase (TPP-effect) has been used in a majority of studies, and its use seems to prevail without consideration of the proportion (latency) as a better alternative. In this letter, the statistical properties of the two measures are compared in the context of a thiamine-dependent enzyme. Proportion is a more bal-anced and sensitive measure than relative increase, and simulation shows that proportion is associated with equal or high-er statistical power than relative increase. The power difference can be as high as 0.12.

scholarly journals A Fully-Adjusted Two-Stage Procedure for Rank Normalization in Genetic Association Studies

2018 ◽  
Author(s):  
Tamar Sofer ◽  
Xiuwen Zheng ◽  
Stephanie M. Gogarten ◽  
Cecelia A. Laurie ◽  
Kelsey Grinde ◽  
...  
Keyword(s):  
Statistical Power ◽  
Type I Error ◽  
Association Studies ◽  
Genetic Association Studies ◽  
Statistical Properties ◽  
Type I ◽  
Residual Distribution ◽  
Two Stage ◽  
Trait Distribution ◽  
Error Rate Control

AbstractWhen testing genotype-phenotype associations using linear regression, departure of the trait distribution from normality can impact both Type I error rate control and statistical power, with worse consequences for rarer variants. While it has been shown that applying a rank-normalization transformation to trait values before testing may improve these statistical properties, the factor driving them is not the trait distribution itself, but its residual distribution after regression on both covariates and genotype. Because genotype is expected to have a small effect (if any) investigators now routinely use a two-stage method, in which they first regress the trait on covariates, obtain residuals, rank-normalize them, and then secondly use the rank-normalized residuals in association analysis with the genotypes. Potential confounding signals are assumed to be removed at the first stage, so in practice no further adjustment is done in the second stage. Here, we show that this widely-used approach can lead to tests with undesirable statistical properties, due to both a combination of a mis-specified mean-variance relationship, and remaining covariate associations between the rank-normalized residuals and genotypes. We demonstrate these properties theoretically, and also in applications to genome-wide and whole-genome sequencing association studies. We further propose and evaluate an alternative fully-adjusted two-stage approach that adjusts for covariates both when residuals are obtained, and in the subsequent association test. This method can reduce excess Type I errors and improve statistical power.

scholarly journals Oscillatory Characteristics of Nociceptive Responses in the SII Cortex

2008 ◽  
Vol 35 (5) ◽  
pp. 630-637 ◽  
Author(s):  
Fu-Jung Hsiao ◽  
Wei-Ta Chen ◽  
Kwong-Kum Liao ◽  
Zin-An Wu ◽  
Low-Tone Ho ◽  
...  
Keyword(s):  
Statistical Power ◽  
Stimulus Onset ◽  
Pain Level ◽  
Thulium Laser ◽  
Current Dipole ◽  
Left Hand ◽  
Power Difference ◽  
Nociceptive Responses ◽  
Cortical Responses ◽  
Pain Stimuli

Objective:This study is aimed to explore the frequency characteristics of pain-evoked neuromagnetic responses in the secondary somatosensory (SII) cortices.Methods:Thulium-laser nociceptive stimuli to the left hand dorsum of 10 right-handed healthy adults. The pain stimuli were rated as mild, moderate, and severe levels according to subjects' reports on a 10-point visual analog scale. We analyzed their cortical responses with wavelet-based frequency analyses and equivalent current dipole (ECD) modeling.Results:For each pain level, we found an increase of theta (4-8 Hz) and alpha (8-13 Hz) power in bilateral SII areas at 180-210 ms after stimulus onset. The power was larger for the moderate than for the mild pain level (p < 0.05), but there was no statistical power difference of these oscillations between moderate and severe pain stimulus conditions (p = 0.7). Within the SII area, we did not observe particular difference in theta and alpha ECD locations between varying pain level conditions.Conclusions:The 4-13 Hz activities, peaking from 180 to 210 ms, are oscillatory correlates of SII activation in response to nociceptive stimulation, but their power may code the magnitude of pain stimuli only up to moderate level, as rated subjectively. This measure could be potentially used to evaluate SII activation in further pain studies.

scholarly journals Handling Missing Entries in Monitoring a Woman’s Monthly Cycle and Controlling Fertility

2018 ◽  
Vol 56 (1) ◽  
pp. 75-90
Author(s):  
Anna Łupińska-Dubicka
Keyword(s):  
Statistical Power ◽  
Dynamic Bayesian Network ◽  
Missing Observations ◽  
Fertility Awareness ◽  
Average Percentage ◽  
Fertile Window ◽  
Bayesian Network Modeling ◽  
Two Measures ◽  
Monthly Cycle

Abstract Even a small percentage of missing data can cause serious problems with analysis, reducing the statistical power of a study and leading to wrong conclusions being drawn. In the case of monitoring a woman’s monthly cycle, missing entries can appear even in a woman experienced in fertility awareness methods. Due to the fact that in a system of controlling a woman’s fertility, it is the most important to predict the day of ovulation and, ultimately, to determine the fertile window as much precisely as possible, much attention should be paid to the quality of the used data. This paper presents the results of handling missing observations as far as predicting the time during the cycle when a woman can become pregnant is concerned. Data taken from a multinational European study of daily fecundability was used to learn the quantitative part of the variety of a higher-order dynamic Bayesian network modeling a woman’s monthly cycle. The main goal of this paper is to examine whether omitting observations has an influence on the model’s reliability. The accuracy of comparison was examined based on two measures: the average percentage length of the infertile time during the monthly cycle and average percentage of days inside the fertile window classified as infertile.

Multiple Testing and Statistical Power With Modified Bonferroni Procedures

1997 ◽  
Vol 22 (4) ◽  
pp. 389-406 ◽  
Author(s):  
Stephen Olejnik ◽  
Jianmin Li ◽  
Suchada Supattathum ◽  
Carl J. Huberty
Keyword(s):  
Multiple Testing ◽  
Statistical Power ◽  
Type I Error ◽  
Average Power ◽  
Simulated Data ◽  
Type I ◽  
Correlation Matrices ◽  
Bonferroni Procedure ◽  
Power Difference ◽  
The Difference

The difference in statistical power between the original Bonferroni and five modified Bonferroni procedures that control the overall Type I error rate is examined in the context of a correlation matrix where multiple null hypotheses, H0 : ρ ij = 0 for all i ≠ j, are tested. Using 50 real correlation matrices reported in educational and psychological journals, a difference in the number of hypotheses rejected of less than 4% was observed among the procedures. When simulated data were used, very small differences were found among the six procedures in detecting at least one true relationship, but in detecting all true relationships the power of the modified Bonferroni procedures exceeded that of the original Bonferroni procedure by at least .18 and by as much as .55 when all null hypotheses were false. The power difference decreased as the number of true relationships decreased. Power differences obtained for the average power were of a much smaller magnitude but still favored the modified Bonferroni procedures. For the five modified Bonferroni procedures, power differences less than .05 were typically observed; the Holm procedure had the lowest power, and the Rom procedure had the highest.

THE VARIANCE AND THE ALGORITHMIC COMPLEXITY OF HEART RATE VARIABILITY DISPLAY DIFFERENT RESPONSES TO ANESTHESIA

1996 ◽  
Vol 06 (11) ◽  
pp. 2169-2172 ◽  
Author(s):  
R.J. STORELLA ◽  
Y. SHI ◽  
H.W. WOOD ◽  
M.A. JIMÉNEZ-MONTAÑO ◽  
A.M. ALBANO ◽  
...  
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
Cardiac Surgery ◽  
Cardiovascular System ◽  
Clinical Data ◽  
Biological Systems ◽  
Biological Data ◽  
Algorithmic Complexity ◽  
Sensitive Measure ◽  
Two Measures

In this study, the variance (a distribution-determined measure of disorder) and the algorithmic complexity (a sequence-sensitive measure) were used to characterize heart rate variability before, during and after cardiac surgery. While it is easy to construct mathematical examples where variance and complexity respond differently to parameter changes, this contrasts with the comparative lack of such examples from biological data. The results presented here provide an example, based on clinical data, where the pattern of changes displayed by the complexity is significantly different from the pattern seen in the variance. While complexity recovers to pre-anesthetic levels following cardiac surgery, variance does not. The details of this pattern suggest that of the two measures, complexity may be the more appropriate metric for characterizing changes in the cardiovascular system in response to anesthetics. The findings reported here demonstrate that measurement of complexity can reveal dynamical changes in biological systems not detected by distribution determined measures such as variance.

Resolution assessment from spectral signal-to-noise ratios

1987 ◽  
Vol 45 ◽  
pp. 746-747
Author(s):  
M. Unser ◽  
B.L. Trus ◽  
A.C. Steven
Keyword(s):  
Electron Microscopy ◽  
Limiting Factor ◽  
Biological Macromolecules ◽  
Signal To Noise ◽  
Differential Phase ◽  
Traditional Measure ◽  
Spectral Signal ◽  
Two Measures ◽  
Diffraction Patterns ◽  
Averaging Techniques

Since the resolution-limiting factor in electron microscopy of biological macromolecules is not instrumental, but is rather the preservation of structure, operational definitions of resolution have to be based on the mutual consistency of a set of like images. The traditional measure of resolution for crystalline specimens in terms of the extent of periodic reflections in their diffraction patterns is such a criterion. With the advent of correlation averaging techniques for lattice rectification and the analysis of non-crystalline specimens, a more general - and desirably, closely compatible - resolution criterion is needed. Two measures of resolution for correlation-averaged images have been described, namely the differential phase residual (DPR) and the Fourier ring correlation (FRC). However, the values that they give for resolution often differ substantially. Furthermore, neither method relates in a straightforward way to the long-standing resolution criterion for crystalline specimens.

Visual Evoked-Response Correlates of Speechreading Performance in Normal-Hearing Adults

1983 ◽  
Vol 26 (1) ◽  
pp. 2-9 ◽  
Author(s):  
Vincent J. Samar ◽  
Donald G. Sims
Keyword(s):  
Multiple Correlation Coefficient ◽  
Evoked Response ◽  
Multiple Correlation ◽  
Potential Significance ◽  
Visual Evoked Response ◽  
Latency Measure ◽  
Two Measures ◽  
Components Analysis ◽  
The Relationship ◽  
Visual Evoked

The relationship between the latency of the negative peak occurring at approximately 130 msec in the visual evoked-response (VER) and speechreading scores was investigated. A significant product-moment correlation of -.58 was obtained between the two measures, which confirmed the fundamental effect but was significantly weaker than that previously reported in the literature (-.90). Principal components analysis of the visual evoked-response waveforms revealed a previously undiscovered early VER component, statistically independent of the latency measure, which in combination with two other components predicted speechreading with a multiple correlation coefficient of S4. The potential significance of this new component for the study of individual differences in speechreading ability is discussed.

Reaction Time and Brain Waves in Omitted Stimulus Tasks

2010 ◽  
Vol 24 (1) ◽  
pp. 1-6 ◽  
Author(s):  
Oscar H. Hernández ◽  
Muriel Vogel-Sprott
Keyword(s):  
Reaction Time ◽  
Cognitive Processes ◽  
Young Male ◽  
Event Related Potential ◽  
Auditory Stimuli ◽  
Motor Action ◽  
Cognitive Component ◽  
Sensory Modalities ◽  
Two Measures ◽  
Somatosensory Stimuli

A missing stimulus task requires an immediate response to the omission of a regular recurrent stimulus. The task evokes a subclass of event-related potential known as omitted stimulus potential (OSP), which reflects some cognitive processes such as expectancy. The behavioral response to a missing stimulus is referred to as omitted stimulus reaction time (RT). This total RT measure is known to include cognitive and motor components. The cognitive component (premotor RT) is measured by the time from the missing stimulus until the onset of motor action. The motor RT component is measured by the time from the onset of muscle action until the completion of the response. Previous research showed that RT is faster to auditory than to visual stimuli, and that the premotor of RT to a missing auditory stimulus is correlated with the duration of an OSP. Although this observation suggests that similar cognitive processes might underlie these two measures, no research has tested this possibility. If similar cognitive processes are involved in the premotor RT and OSP duration, these two measures should be correlated in visual and somatosensory modalities, and the premotor RT to missing auditory stimuli should be fastest. This hypothesis was tested in 17 young male volunteers who performed a missing stimulus task, who were presented with trains of auditory, visual, and somatosensory stimuli and the OSP and RT measures were recorded. The results showed that premotor RT and OSP duration were consistently related, and that both measures were shorter with respect to auditory stimuli than to visual or somatosensory stimuli. This provides the first evidence that the premotor RT is related to an attribute of the OSP in all three sensory modalities.

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