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PubMedDate not supplied

The choice between analysis of variance and analysis of covariance with special reference to the analysis of organ weights in toxicology studies.

The problem of when to include a covariate in the analysis of variance is considered in the special case of organ weight analysis in animal toxicology studies. The covariate is bodyweight prior to death, which may be subject to treatment effects. A simulation study is carried out to compare four rules for deciding whether or not to include the covariate. It is concluded that if there is background information which shows a linear relationship between variate and covariate it is advisable to adjust for the covariate, however weak the relationship may appear to be on the current set of data. Alternative procedures lead to unacceptably high Type I error rates.

Analysis of Variance↗
PubMed1995

Segregation analysis and variance components analysis of bone mineral density in healthy families.

Bone mineral density (BMD) was measured in 1992-93 in 129 nuclear families, including 258 parents and 183 children, and was analyzed for familial resemblance factors. BMD measurements were adjusted on weight and age. Segregation analysis rejected the monogenic hypothesis and exhibited a strong polygenic component. Variance components analysis was then used to estimate the parameters of a multivariate normal model including an additive polygenic component, a common environment factor, and a residual specific to each individual. The genetic component was independent of sex and age. The common environmental factor was not significant. The variance of the residual specific factor appeared to be a quadratic function of age, reaching its minimum value at 26.4 years. Consequently, the maximum value for heritability (ratio of genetic variance to total variance) is observed at this age (h2 = 0.84). According to this model, the correlation between two relatives is a function of the ages of each individual in the pair.

Adolescent↗
PubMed1995

Commentary and opinion: I. Principal component analysis, variance partitioning, and "functional connectivity".

We briefly review the need for careful study of "variance partitioning" and "optimal model selection" in functional positron emission tomography (PET) data analysis, emphasizing the use of principal component analysis (PCA) and the importance of data analytic techniques that allow for heterogeneous spatial covariance structures. Using an [15O]water dataset, we demonstrate that--even after data processing--the intrasubject signal component of primary interest in baseline activation studies constitutes a very small fraction of the intersubject variance. This small intrasubject variance component is subtly but significantly changed by using analysis of covariance instead of scaled subprofile model processing before applying PCA. Finally, we argue that the concept of "functional connectivity" should be interpreted very generally until the relative roles of inter- and intrasubject variability in both disease and normal PET datasets are better understood.

Analysis of Variance↗
PubMed1994

Variance analysis of gamma-aminobutyric acid (GABA)-ergic inhibitory postsynaptic currents from melanotropes of Xenopus laevis.

We have studied the variance in the decay of large spontaneous gamma-aminobutyric acid (GABA)-ergic inhibitory postsynaptic currents (IPSCs) in melanotropes of Xenopus laevis to obtain information about the number of GABAA receptor channels that bind GABA during the IPSCs. The average decay of the IPSCs is well described by the sum of two exponential functions. This suggests that a three-state Markov model is sufficient to describe the decay phase, with one of the three states being an absorbing state, entered when GABA dissociates from the GABAA receptor. We have compared the variance in the decay of large spontaneous IPSCs with the variance calculated for two different three-state models: a model with one open state, one closed state, and one absorbing state (I), and a model with two open states and one absorbing state (II). The data were better described by the more efficient model II. This suggests that the efficacy of GABA at synaptic GABAA receptor channels is high and that only a small number of channels are involved in generating the GABA-ergic IPSCs.

Analysis of Variance↗
PubMed1992

Variance analysis refines overhead cost control.

Many healthcare organizations may not fully realize the benefits of standard cost accounting techniques because they fail to routinely report volume variances in their internal reports. If overhead allocation is routinely reported on internal reports, managers can determine whether billing remains current or lost charges occur. Healthcare organizations' use of standard costing techniques can lead to more realistic performance measurements and information system improvements that alert management to losses from unrecovered overhead in time for corrective action.

Accounting↗
PubMed1986

Variance analysis by use of a low cost desk top calculator.

A simple program for an HP-97 desk top calculator, which can be adapted to an HP-67, is presented. This program detects the presence of an added component of variance in any series classified with a unique criterion. Each series can be formed by any number of data. The program supplies additional information about this component. A brief theoretical description and a practical example are also included.

Analysis of Variance↗
PubMed1989

Variance analysis of excitatory postsynaptic potentials in cat spinal motoneurons during posttetanic potentiation.

1. Fluctuations in the peak amplitudes of composite excitatory postsynaptic potentials (EPSPs) in cat spinal motoneurons were analyzed during posttetanic potentiation (PTP). Each of a series of identical tetanic stimulus trains delivered to a muscle nerve was followed by 45 test stimuli applied at 2-s intervals. The mean peak amplitude and mean peak variance were calculated for EPSPs evoked by all those stimuli following a tetanus with the same time interval. It was assumed that the variance arises primarily from the probabilistic all-or-none behavior of single synaptic boutons and background noise due to spontaneous synaptic activity and thermal noise in the recording system. The variance was corrected for the contribution from additive Gaussian background noise. 2. If it is assumed that individual synaptic boutons behave independently, corrected mean peak variance and mean peak amplitude are related by a parabolic function. The expected parabolic relationship was seen in 9 of 31 cases studied, and the parameters of the best parabolic fit to the data allowed estimation of some synaptic properties. From these parameters, the mean amplitude of the unit EPSP (v) was estimated to be 102.1 +/- 57.4 (SD) microV. An average of 3.7 boutons comprised each Ia-motoneuron contact system. 3. On average, only 27% of all synaptic boutons given off by the stimulated Ia fibers to one motoneuron were active and releasing transmitter during unpotentiated reflex transmission. The remaining 73% of the synapse population was intermittently silent. The population of boutons which took part in synaptic transmission could be divided into two subpopulations, one with a release probability P = 1 and a second with a mean release probability P = 0.13 +/- 0.086. 4. We conclude that synaptic boutons connecting Ia afferents to motoneurons exist in two populations, one having a high and one a low probability of transmitter release. Transmitter release is quantal, resulting in a unit EPSP of approximately 100 microV measured at the motoneuron soma.

Analysis of Variance↗
PubMedDate not supplied

Patient population management: taking the leap from variance analysis to outcomes measurement.

Case managers today at BCHS have a somewhat different role than at the onset of the Collaborative Practice Model. They are seen throughout the organization as: Leaders/participants on cross-functional teams. Systems change agents. Integrating/merging with quality services and utilization management. Outcomes managers. One of the major cross-functional teams is in the process of designing a Care Coordinator role. These individuals will, as one of their functions, assume responsibility for daily patient care management activities. A variance tracking program has come into the Utilization Management (UM) department as part of a software package purchased to automate UM work activities. This variance program could potentially be used by the new care coordinators as the role develops. The case managers are beginning to use a Decision Support software, (Transition Systems Inc.) in the collection of data that is based on a cost accounting system and linked to clinical events. Other clinical outcomes data bases are now being used by the case manager to help with the collection and measurement of outcomes information. Hoshin planning will continue to be a framework for defining and setting the targets for clinical and financial improvements throughout the organization. Case managers will continue to be involved in many of these system-wide initiatives. In the words of Galileo, 1579, "You need to count what's countable, measure what's measurable, and what's not measurable, make measurable."

Analysis of Variance↗