Biomedical subjects

R G Staudte

Publications and source records attributed to R G Staudte.

7 recordsLinked to original sources

PubMed2006

Interval estimates of weighted effect sizes in the one-way heteroscedastic ANOVA.

A framework for comparing normal population means in the presence of heteroscedasticity and outliers is provided. A single number called the weighted effect size summarizes the differences in population means after weighting each according to the difficulty of estimating their respective means, whether the difficulty is due to unknown population variances, unequal sample sizes or the presence of outliers. For an ANOVA weighted for unequal variances, we find interval estimates for the weighted effect size. In addition, the weighted effect size is shown to be a monotone function of a suitably defined weighted coefficient of determination, which means that interval estimates of the former are readily transformed into interval estimates of the latter. Extensive simulations demonstrate the accuracy of the nominal 95% coverage of these intervals for a wide range of parameters.

Analysis of Variance↗

PubMed1997

Estimating clonal heterogeneity and interexperiment variability with the bifurcating autoregressive model for cell lineage data.

We utilize an extension of the variance-components models for cell lineage data in Huggins and Staudte (R.M. Huggins and R.G. Staudte, Variance components models for dependent cell populations. J. Am. Stat. Assoc. 89:19-29 (1994) to analyze NIH3T3 cells grown in two different media. This modeling approach has the advantage of a simple built-in correlation structure between familial members and allows for estimating experimental effects, rather than treating them as random effects. In addition, this methodology gives robust estimates of model parameters together with standard errors required for statistical inference. The importance of clonal heterogeneity and interexperiment variability in modeling eukaryotic cell cycles was previously pointed out by Kuczek and Axelrod (T. Kuczek and D.E. Axelrod, The importance of clonal heterogeneity and interexperimental variability in modeling the eukaryotic cell cycle. Math. Biosci. 79:87-96 (1986). This analysis confirms significantly positive sister-sister correlation when cells are grown in rich or poor medium and negative mother-daughter correlation when cells are grown in poor medium. However, for cells grown in rich medium, Kuczek and Axelrod's analysis gives negative mother-daughter correlations, whereas this analysis gives significant positive mother-daughter correlations.

3T3 Cells↗

PubMed1997

Weighing the evidence for hypotheses with small samples of right-censored exponential data.

The p-value evidence for an alternative to a null hypothesis regarding the mean lifetime can be unreliable if based on asymptotic approximations when there is only a small sample of right-censored exponential data. However, a guarded weight of evidence for the alternative can always be obtained without approximation, no matter how small the sample, and has some other advantages over p-values. Weights of evidence are defined as estimators of 0 when the null hypothesis is true and 1 when the alternative is true, and they are judged on the basis of the ensuing risks, where risk is mean squared error of estimation. The evidence is guarded in that a pre-assigned bound is placed on the risk under the hypothesis. Practical suggestions are given for choosing the bound and for interpreting the magnitude of the weight of evidence. Acceptability profiles are obtained by inversion of a family of guarded weights of evidence for two-sided alternatives to point hypotheses, just as confidence intervals are obtained from tests; these profiles are arguably more informative than confidence intervals, and are easily determined for any level and any sample size, however small. They can help understand the effects of different amounts of censoring. They are found for several small size data sets, including a sample of size 12 for post-operative cancer patients. Both singly Type I and Type II censored examples are included. An examination of the risk functions of these guarded weights of evidence suggests that if the censoring time is of the same magnitude as the mean lifetime, or larger, then the risks in using a guarded weight of evidence based on a likelihood ratio are not much larger than they would be if the parameter were known.

Confidence Intervals↗

PubMed1996

A reexamination of the cell-lineage data of E. O. Powell.

E. O. Powell carried out numerous experiments observing cell-generation times on bacteria. His statistical methodology, though quite advanced 40 years ago, can be enhanced by better models of dependence, by advanced computational methods, and by judicious use of robust methods. We reexamine Powell's data, focussing on his main interest in establishing whether there were indeed dependencies in generation times between cells with close filial connections.

Analysis of Variance↗

PubMed1992

A bifurcating autoregression model for cell lineages with variable generation means.

The bifurcating autoregression model for cell lineage data is extended to allow for observations whose means vary from generation to generation. The maximum likelihood estimates of this extended model are found and used to estimate the generation means and overall variance. The model is also used to test for inherited effects as measured by mother-daughter correlation, and for environmental effects as measured by the sister-sister correlation, conditional on inherited effects. Applications to data sets on EMT6 cells and Escherichia coli are given.

Animals↗

PubMed1984

Additive models for dependent cell populations.

We propose an additive model for cell population growth which allows for positive correlation between sister cell lifetimes but arbitrary correlations between mother and daughter cell lifetimes. In the model each cell lifetime is the sum of two independent components, one of which is shared with its sister cell and which is also a function of the components of the lifetime of their mother. Assuming that the components follow a gamma distribution, the model is fitted to cell lifetime data of EMT6 cells obtained by the method of time-lapse cinematography.

Animals↗

PubMed1982

Planning blocked mitosis experiments for efficient estimation of population-doubling time and cell-cycle time.

In this paper the standard errors of both classical and recently proposed estimators of mean population-doubling time and mean cell-cycle time are derived as functions of the number of cells counted and the counting times in a blocked mitosis experiment. Practical suggestions are made regarding the allocation of cell counts that will reduce the standard errors. It is shown that the proposal of Jagers (1977, Bulletin of the International Statistical Institute 47 (2), 418-422) for estimating cell-cycle time yields, quite generally, smaller standard error than do the classical estimators. Finally, a relationship between the mean and variance of cell-cycle time and the mean doubling time is derived; in some cases this relationship justifies the classical identification of mean doubling time and mean cycle time.

Cell Cycle↗