Variance Index Research Articles

Cervical accelerometry in preterm infants with and without bronchopulmonary dysplasia

Cervical accelerometry with digital signal processing (DSP) can identify signals that are consistently associated with swallowing during feeding of infants. It is shown that these signals, called initial discrete sounds (IDSs), become more uniform with advancing postmenstrual age (PMA) in healthy preterm infants. The objectives of this study were to determine if cervical accelerometry and DSP at a higher sample rate than previously used (22kHz versus 16kHz), in conjunction with a DSP software package that allows manipulation of the sound files, would improve the accuracy of the previously developed variance index (VI) method of analyzing accelerometric information. The modified VI method was then used to measure developmental differences in the IDS morphology of infants with and without bronchopulmonary dysplasia (BPD). VIs were calculated for 24 feeding studies of infants of between 32 and 39 weeks PMA: 12 studies on healthy preterm infants (n=10: three males, seven females; mean gestational age [GA] 28.6 weeks, SD 0.4; mean birth weight [BW] 1080g, SD 82; PMA mean 35.2 weeks, SD 0.6) and 12 studies on infants with BPD (n=7: five males, two females; GA 27.1 weeks, SD 0.4; BW 911g, SD 71; PMA 36.2 weeks, SD 0.6). There was a significant inverse correlation between VI and PMA for the healthy preterm group (r=0.66, m=‐2.31/week, p=0.02). There was no significant correlation between VI and PMA for the BPD cohort. The VI of infants with BPD was significantly different from that of infants without BPD (p< 0.007, multiple regression analysis, interaction PMA×Group). Additionally, using our modified VI technique, 100% of swallows were found to have the expected IDS signals.

Dr. Koenigsberg and Colleagues Reply

Back to table of contents Previous article Next article Letter to the EditorFull AccessDr. Koenigsberg and Colleagues ReplyHAROLD W. KOENIGSBERG, M.D., PHILIP D. HARVEY, Ph.D., VIVIAN MITROPOULOU, M.A., ANTONIA NEW, M.D., MARIANNE GOODMAN, M.D., and LARRY J. SIEVER, M.D., HAROLD W. KOENIGSBERGSearch for more papers by this author, M.D., PHILIP D. HARVEYSearch for more papers by this author, Ph.D., VIVIAN MITROPOULOUSearch for more papers by this author, M.A., ANTONIA NEWSearch for more papers by this author, M.D., MARIANNE GOODMANSearch for more papers by this author, M.D., and LARRY J. SIEVERSearch for more papers by this author, M.D., New York, N.Y.Published Online:1 Feb 2003https://doi.org/10.1176/appi.ajp.160.2.395AboutSectionsView EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail To the Editor: Dr. Links and colleagues report on a study of the correlation of the Affective Lability Scale with a single-item visual analogue scale of affective experience. They note that in their group of 21 outpatients, scores on this single item did not correlate with scores on the scale in a manner that they consider consistent with the validity of the Affective Lability Scale. We appreciate their interest in our scale and share their interest in validation of the Affective Lability Scale in a range of suitable populations. Unfortunately, their study is methodologically weak in at least three areas and yields results that are not germane to our study. There are several major limitations to the study, as well as a number of more minor ones.First, the Affective Lability Scale was designed to study populations with unstable affect. There are no data presented regarding the diagnoses of the small group of subjects reported on and no indication that they come from populations theoretically manifesting affective lability. Our study had 152 patients who were carefully diagnosed with a procedure that included two separate structured diagnostic interviews (the Structured Interview for the Diagnosis of Personality Disorders and the Schedule for Affective Disorders and Schizophrenia) of high reliability. Thus, we compared groups of patients with clear DSM-IV diagnoses of conditions with putative unstable affect (borderline personality disorder) to patients with other personality disorder diagnoses in which stable affect is expected. Thus, the patients of Dr. Link and colleagues are not demonstrated to be in any way similar to ours, and the lack of detail regarding their diagnoses, regardless of reliability, renders their comparison with our study group problematic.Second, the authors used a single item to measure affective experience. They present no data to suggest that this item has suitable test-retest reliability in their group. Both the Affective Lability Scale and the Affect Intensity Measure, the two scales used in our study, have well-documented test-retest reliability (0.84 for the global Affective Lability Scale and 0.81 for the Affect Intensity Measure). With no evidence of test-retest reliability, the most parsimonious explanation of variance over time in scores in patients with stable symptoms is error variance. Error variance due to test-retest unreliability, by definition, cannot correlate with systematic variance associated with reliable scores. Thus, the lack of correlation between an index of error variance (affective lability) and reliable scores on the Affective Lability Scale is completely expected and cannot address the issue of the scale’s validity.Third, there are multiple dimensions of affect, including intensity, instability, and polarity. Our study examined correlations between intensity and instability across polarity of affective experience. Dr. Links and colleagues ignore this well-replicated factor structure and present a single index of affective experience collapsing across three known orthogonal dimensions. They provide no data regarding the convergent and discriminant validity of their index, giving no idea as to what the other correlates of this single-item scale would be. Thus, we have no idea what their scale is measuring.In conclusion, Dr. Links and colleagues, who suggest that their data call into question the validity of the Affective Lability Scale, overinterpret their data. We stand by our results and welcome more methodologically relevant tests of the Affective Lability Scale and other measures of affective instability.Reprints are not available; however, Letters to the Editor can be downloaded at http://ajp.psychiatryonline.org. FiguresReferencesCited byDetailsCited ByNone Volume 160Issue 2 February 2003Pages 395-395 Metrics History Published online 1 February 2003 Published in print 1 February 2003

Tracer mixing dynamics during aggregation and fragmentation

For many chemical systems consisting of particles, liquid droplets, or gas bubbles undergoing concurrent (reversible) aggregation and fragmentation in a stirred immiscible fluid, evolution of the particle distribution and mixing of chemical species are important fundamental issues. A dynamic model for dispersive mixing systems presented here illustrates the time dependence of the particle-size distribution (PSD) and the tracer mass distribution (TMD). For rapid tracer diffusion, the population balance equations (PBEs) for the PSD and TMD are identical (only the initial conditions differ) for binary aggregation and fragmentation rate coefficients that do not depend on particle size or tracer mass. The integrodifferential PBE is solved by a numerical method, and results agree with the moment solution. Measures for the degree of tracer mixing are related to the variance or polydispersity index and to the mixing entropy. The kinetics are reversible, allowing the PSD, TMD, and mixing entropy to approach stationary states. Results are partially compared with a similarity solution for the PSD.

Beat-to-beat repolarization variability measured by T wave spectral variance index in chronic infarcted animals.

Recent experimental and clinical studies have shown that beat-to-beat variability of repolarization morphology is associated with an increased risk for developing malignant ventricular arrhythmias. However, few data exist on the relationship between beat-to-beat repolarization variability and myocardial infarction itself. In the present work we tested the algorithm of T wave spectral variance (TWSV) using the two dimension fast Fourier transform, in an animal model of myocardial infarction to extend the evidences that support the existence of beat-to-beat alteration in repolarization during the chronic stage of myocardial infarction. Thirty-four New Zealand rabbits were included in the study and divided in two groups. Group I (N = 24) exposed to surgical ligation of the left anterior descendent coronary artery. Group II (N = 10) sham operated animals. The TWSV index was calculated before and after 15 and 45 days of surgery. Both groups showed significant increments in TWSV after 15 days postsurgery. However, while the sham animals return to its control value, the infarcted group exhibited values of the TWSV index that remains significantly high after 45 days of surgery, with a mean increment of 28.7% (P < 0.05 against sham). Moreover, when the infarcted group was qualitatively divided in three subgroups, according to its infarction areas, a trend was found in the correlation between the magnitude of the infarcted area and the TWSV index. This noninvasive measure confirms the presence of temporal repolarization variability associated with chronic myocardial infarction and further contributes to identify the infarcted animals.

Cervical accelerometry in preterm infants

The objective of this study was to develop a method to use digital signal processing (DSP) technology to describe quantitatively and statistically swallow‐associated sounds in preterm infants and to use this method to analyze changes as infants mature. Twelve recordings of accelerometric and physiological data on bottle‐feeding preterm infants between 32 and 39 weeks’postmenstrual age (PMA) were analyzed. Cervical auscultation was performed using an accelerometer attached over the larynx. Acoustic data were recorded and graphically displayed using DSP software. Initial discrete sounds (IDSs) were identified and used to construct an average waveform from which a‘variance index’(VI) was calculated for each infant. The shape of the IDS waveforms became progressively more uniform with advancing PMA, as indicated by a significant inverse correlation between VI and PMA (r=0.739;p=0.006). DSP technology facilitated the development of a new method to quantitatively analyze feeding in preterm infants. This method provides an elegant tool to track maturation of infant feeding and assessing feeding readiness. This technique makes the interpretation of cervical auscultation data less subjective by replacing the verbal description of the sounds of feeding with quantitative numeric values. It is anticipated that this method can be automated to facilitate further the analysis of cervical accelerometry data.

Body weight changes and the A-6G polymorphism of the angiotensinogen gene.

The objective of the study was to analyze the relationship of polymorphisms of the angiotensinogen gene with changes in body weight during 3 y of antihypertensive treatment, in a group of young adults with essential hypertension. Essential hypertensives, less than 50 y old, never previously treated with antihypertensive drugs and in the absence of diabetes mellitus were included. After the initial evaluation, patients were treated using only non-pharmacological measures (n=29), beta-blockers (n=40) or angiotensin-converting enzyme inhibitors (n=66). Resting blood pressure, biochemical profile and body weight at the beginning and yearly were measured. The polymorphism A-6G of the angiotensinogen gene located in the promoter region was analyzed. One-hundred and thirty-five patients were included. Genotypes of the A-6G polymorphism of the AGT gene were in Hardy-Weinberg equilibrium (AA 34, AG 63, GG 38). No significant differences were observed among genotypes in terms of age, body mass index, body weight, systolic or diastolic blood pressure. No significant differences in the genotype distribution or in the allele frequencies were observed, although the A allele was most frequent among the obese subjects. During the 3 y of antihypertensive treatment, there was a trend to increase weight despite the dietary recommendations. The slopes of body weight over time, adjusted by age and baseline BMI, differed significantly among the homozygote genotypes (P=0.006). The highest were for those with the AA genotype and the lowest for the GG genotype (1.180+/-0.25 and -0.128+/-0.24 kg/y; P=0.0001). The influence of the genotype in the changes on body weight remained significant after considering its interaction with the kind of antihypertensive treatment, although among subjects carrying the AA genotype those treated with ACEi showed the least body weight change. Furthermore, A-6G genotypes had the largest influence on weight changes, accounting for 19% of the variance, when age, sex and initial body mass index were included in the model. In a group of young adult hypertensive subjects, there was a trend to increase weight despite dietary recommendations. Subjects with the AA genotype were those with the largest weight gain, but this effect was modified by the antihypertensive treatment.

Multiple Indices of Northern Hemisphere Cyclone Activity, Winters 1949–99

The National Centers for Environmental Prediction‐National Center for Atmospheric Research (NCEP‐NCAR) reanalysis is used to estimate time trends of, and analyze the relationships among, six indices of cyclone activity or forcing for the winters of 1949‐99, over the region 208‐708N. The indices are Eady growth rate and temperature variance, both at 500 hPa; surface meridional temperature gradient; the 95th percentile of near-surface wind speed; and counts of cyclones and intense cyclones. With multiple indices, one can examine different aspects of storm activity and forcing and assess the robustness of the results to various definitions of a cyclone index. Results are reported both as averages over broad spatial regions and at the resolution of the NCEP‐NCAR reanalysis grid, for which the false discovery rate methodology is used to assess statistical significance. The Eady growth rate, temperature variance, and extreme wind indices are reasonably well correlated over the two major storm track regions of the Northern Hemisphere as well as over northern North America and Eurasia, but weakly correlated elsewhere. These indices show moderately strong correlations with each of the two cyclone count indices over much of the storm tracks when the count indices are offset 7.58 to the north. Regional averages over the Atlantic, the Pacific, and Eurasia show either no long-term change or a decrease in the total number of cyclones; however, all regions show an increase in intense cyclones. The Eady growth rate, temperature variance, and wind indices generally increase in these regions. On a finer spatial scale, these three indices increase significantly over the storm tracks and parts of Eurasia. The intense cyclone count index also increases locally, but insignificantly, over the storm tracks. The wind and intense cyclone indices suggest an increase in impacts from cyclones, primarily over the oceans.

Significance tables for the exact variance test for the Poisson distribution with alternative underdispersion

Fisher (1950) introduced the variance or dispersion index test statistic to test deviations of the Poisson distribution. For this test approximate critical values exist for large sample sizes. If the number of observations is small this approximation can lead to a wrong conclusion. For small samples, the exact critical values can only be derived by enumeration of all possibilities. Tables of critical values for overdispersion already exist (e.g., Rao and Chakravarti, 1956) However, in many biological situations underdispersion, a more-regular-than-Poisson distribution, is a common phenomenon. Therefore, we have tabulated in this paper the one-tailed critical values for a small number of observations under the null hypothesis (H0) that the random variable is Poisson distributed against the alternative hypothesis of underdispersion. With the help of this table, the hypothesis that the observations in a data set are Poisson distributed, can be tested easily with the variance test. The tables are illustrated with examples from the literature and some observations from our own research. In general, the χ2 approximation gives a smaller significance level than the exact variance test.

Characterization of Mixing in a Stirred Tank by Planar Laser Induced Fluorescence (P.L.I.F.)

The mixing of two water feedstreams is investigated in a 0.02m 3 continuous stirred tank, from concentration measurements. These measurements are carried out with a laser sheet in a very thin vertical plane through the vessel tangent to the impeller. The proportionality between the grey level obtained by planar laser induced fluorescence and the local concentration has been previously determined. The fields of instantaneous concentration, temporal variance and mixing index are processed from the grey level images.

Within‐population craniometric variability of insular populations of deer mice, Peromyscus maniculatus, elucidated by landscape configuration

Within‐population genetic variability of twelve insular and four mainland populations of deer mice (Peromyscus maniculatus) was assessed using craniometric characters, and compared to results previously obtained from RAPD data. An index of Craniometric Variance (CVar) was computed from pairwise distances among all specimens. Variations in CVar measures were then compared to landscape variables using a linear regression approach. Our results suggest that CVar decreases in presence of large number of a competitive species (the boreal redback vole, Clethrionomys gapperi; r=−0.527, p&lt;0.037) in deer mouse populations. Island remoteness (r=−0.251, p&lt;0.220) and the geometry of the bank opposite to each island (r=−0.459, p&lt;0.067) were marginally correlated with CVar, but the linear combination of these two variables, forming a composite isolation index, represented the major factor explaining the observed CVar (r=−0.648, p&lt;0.011). Using a multiple regression model, 76.3% of the CVar was explained by a combination of this isolation index and the competitors’ abundance. These results suggest that taking into account landscape barriers as well as the dispersal behavior of small mammals might provide sounder ecological variables than geographical distances alone for predicting within‐population genetic variability in a network of habitat patches.

Comparisons of high-frequency acoustic and shallow-water ocean temperature fluctuations

Dynamic ocean processes produce spatial and temporal fluctuations in the ocean’s index of refraction along the propagation path that cause acoustic propagation fluctuations. This paper reports a second set of measurements designed to determine environmental limits on ping-to-ping amplitude and phase variability of direct path acoustic fluctuations in very shallow water. In September 1997, the Naval Research Laboratory in conjunction with the NATO SACLANT Undersea Research Centre conducted this series of experiments, in shallow water off American Beach, located between Pisa and Livorno, Italy. Established equations for the variance of the acoustic amplitude and phase as a function of the index of refraction variance and the ocean characteristic length scale under conditions of isotropic turbulence are used to predict acoustic fluctuations for comparison with measurements. In these results, measured phase fluctuations are more consistent with sea swell predictions than isotropic turbulence predictions. Phase fluctuations are relatively insensitive to water column stability and anomalous phase fluctuations correlate with wind direction. Amplitude fluctuations are consistent with isotropic turbulence predictions and anomalous amplitude fluctuations correlate with changing stability. [Work supported by ONR.]

Receding-horizon unbiased FIR filters for continuous-time state-space models without a priori initial state information

A receding horizon unbiased finite-impulse response filter (RHUFF) is proposed for continuous-time state space models. Linearity, unbiasedness, finite-impulse response (FIR) structure, and independence of the initial state information will be required in advance, in addition to a performance index of minimum variance. The proposed RHUFF is obtained by directly minimizing the performance index with the unbiasedness constraint. The proposed RHUFF is represented first in a standard FIR form and then in an iterative form. It is shown that the RHUFF is equivalent to the existing receding horizon (RH) Kalman FIR filter. The former is more systematic and logical, while the latter is heuristic due to the handling of infinite covariance of the initial state information.

Controller performance assessment based on minimum and open-loop output variance

The need to achieve reliable and effective automatic control systems has directed numerous research efforts towards the development of monitoring and assessment methods of the closed-loop performance. A new controller assessment index, called relative variance index (RVI) is introduced in this work, according to which the closed-loop performance is compared with the best theoretical control action (minimum variance control) and no control action. For the estimation of RVI, an identification method is employed to extract the system models and an estimate of the process unit delays. The proposed index, RVI, is in agreement with the classical deterministic closed-loop assessment measures and thus can be utilized for the controller performance evaluation more effectively.

Particulate concentration measured from scattered light fluctuations

Scintillation of scattered radiation caused by particulate matter is studied. By use of stochastic theory, expressions for mathematical expectation, variance, and scintillation index are derived. A method of measuring particulate-mass concentration with the scintillation index is proposed. The major advantage of this method is its insensitivity to lens contamination and particle-color change.

Laboratory Accreditation The Next Generation of Quality Improvement in Thailand

A Thailand quality assessment program called iThe External Quality Assessment in Clinical Chemistry, EQAC” was found in 1986. A blind lyophilized control serum is monthly-cycle distributed to the participants and the returned test-report values are evaluated by a computed program. Evaluated report Mean Variance Index Scores (MVIS) and mean score of all tests are posted back to the participants.In 1999 the program was applied by 324 laboratory participants of which 59% of general hospital and community health hospital laboratory, 29% of private hospital laboratory including polyclinics, and 12% of the others. By now as many as 144 trials of 23 biochemistry tests at different methods were assessed from the EQAC program. Participant communication, knowledge update and enhanced quality encouragement have been managed by mean of participants' VIS from 120 to 93 during 1987–1998.For the next millennium, the implementation of ISO/IEC Guide 25 for quality system in clinical laboratory will be a promising strategy...

Laboratory Accreditation the Next Generation of Quality Improvement in Thailand

A Thailand quality assessment program called ìThe External Quality Assessment in Clinical Chemistry, EQAC” was found in 1986. A blind lyophilized control serum is monthly-cycle distributed to the participants and the returned test-report values are evaluated by a computed program. Evaluated report Mean Variance Index Scores (MVIS) and mean score of all tests are posted back to the participants. In 1999 the program was applied by 324 laboratory participants of which 59% of general hospital and community health hospital laboratory, 29% of private hospital laboratory including polyclinics, and 12% of the others. By now as many as 144 trials of 23 biochemistry tests at different methods were assessed from the EQAC program. Participant communication, knowledge update and enhanced quality encouragement have been managed by mean of participants' VIS from 120 to 93 during 1987–1998. For the next millennium, the implementation of ISO/IEC Guide 25 for quality system in clinical laboratory will be a promising strategy of quality improvement in Thailand. The Ministry of Public Health is step forward to adopt this guide for certifying standard laboratories. These efforts will be a first step towards the next generation of quality improvement for clinical laboratory in Thailand.

The Contribution of the Zimbabwe External Quality Assessment Schemein the Practice of Laboratory Medicine: 1989–1999

The Department of Chemical Pathology of the University of Zimbabwe (Medical School) has set up an external quality assurance scheme, Zimbabwe External Quality Assessment Scheme (ZEQAS) to assess the quality of clinical chemistry laboratory performance in Zimbabwe. The programme has been in place since 1989. 43 clinical chemistry laboratories, both public and private, are currently participating in the quality assessment scheme. Analytical laboratory performance for participants is examined for twelve analytes. A standardized computer software package is used to process data and for producing performance charts. The information highlighted by a computer print-out for each participating laboratory includes the following: MRVIS (mean running variance index score) for all analytes, overall MRVIS for the laboratory, table of results for each analyte (with its mean value and cofficient of variation) and trimmed results for each analyte by individual method which include number of laboratories using a particular method, mean results for that particular method, SD (standard deviation) for that particular method and CV (coefficient of variation) for that particular method. Since the introduction of ZEQAS, there has been a drastic improvement in clinical chemistry laboratory performance in Zimbabwe. The overall mean running variance index score (OMRVIS) for all laboratories over a period from 1990 to 1999 has improved from 163 to 98.

A Control Performance Index Based on Minimum and Open-Loop Output Variance

The need to achieve reliable and effective automatic control systems has directed numerous research efforts towards the development of monitoring and assessment methods of the closed-loop performance. A new controller assessment index, called Relative Variance Index or RVI, is introduced in this work, according to which the closed loop performance is compared with the theoretically best control action (minimum variance control) and no control action. For the estimation of RVI, an identification method is employed to extract the system models and an estimate of the process unit delays. The proposed index, RVI, is in agreement with the classical deterministic closed-loop assessment measures and thus can be utilized for the controller performance evaluation more effectively.

Diagnosis of renovascular disease by extra- and intrarenal Doppler parameters.

It is still a matter of debate as to which parameters should be used for noninvasive diagnosis of renovascular disease by renal Doppler sonography (RDS). The accuracy of RDS in the detection of renal artery stenosis (RAS) was tested in 95 consecutive, moderate to severe hypertensive patients (I-II World Health Organization [WHO] stages). Reno-aortic ratio (RAR) for peak systolic velocity (PSV) was also calculated to assist in the diagnosis of significant (>50%) RAS. Paired receiver-operating characteristic (ROC) analysis was plotted for evaluating the relationship between sensitivity and specificity for each parameter. In a subset of 57 kidneys, the influence of blood pressure and age on intraparenchymal parameters was evaluated. Measurements of maximal peak systolic velocity (PSV) at the site of stenosis, RAR for PSV, and minimum acceleration index in the main renal artery showed high accuracy (areas under the ROC curve 0.97, 0.88, and 0.80, respectively). Among intraparenchymal parameters, early systolic acceleration showed the best area under the ROC curve (0.90), but provided a low positive predictive value (29%) and was significantly influenced by blood pressure (multiple r=0.56; p=0.001). Pulsatility and resistive indices were found to be less powerful as absolute values, and both significantly influenced by blood pressure and age (multiple r=0.60 and 0.50; p=0.001, p=0.02, respectively). However, interindividual variance of intrarenal indices should be minimized by calculation of side difference, although this procedure would become misleading or impossible in patients with bilateral RAS or a single kidney, respectively. These results support the use of extraparenchymal parameters for noninvasive detection of RAS, and emphasize that intrarenal parameters cannot be considered as absolute values.

Does 360‐degree feedback work in different industries?

In order to determine the usefulness of multi‐source rating in different types of organizations, this study explored differences among organization types in four areas: leniency, interrater agreement, relationships between these ratings and effectiveness, and the relationship between agreement and effectiveness. Used self, subordinate, peer, and supervisor ratings for 1,080 target managers in six types of organizations: education, military, government, manufacturing, finance, and health. Interrater agreement was measured in three ways: an index of variance, a point‐difference categorization method, and categories of self‐other agreement. Results indicated that a leniency bias was present in educational institutions, after controlling for demographic characteristics. Interrater agreement was lowest in government agencies and highest in education and manufacturing organizations. In private sector organizations, more poor‐performing managers tended to over‐estimate their performance relative to the perceptions of others. Interrater agreement was positively related to effectiveness especially in education and finance organizations. Results suggest that multi‐source feedback may work differently in different types of organizations, and such differences may need to be taken into account by researchers, practitioners, and feedback recipients.