Population Variability

The standard deviation as defined relates to the repeatability of measurements on the same sample. When many samples are taken from a large population, sampling variability and population variability terms have to be added to Eq. (1.6) and the interpretation will reflect this. 

Each point in the phase diagram in Fig. 8.8 corresponds to a certain value of a and b, i.e., it represents the possible chemical composition of a molecular population. Variable a forms the horizontal axis, (1 +a) being the number of monomer types. The b axis represents the quality factor of the polymer catalysis. The transition region contains those populations which can have both ordered and disordered... 

Metabolism and pharmacokinetic studies have greater relevance when conducted in both sexes of young adult animals of the same species and strain used for other toxicity tests with the test substance. The number of animals used in metabolism and pharmacokinetic studies would be sufficient to reliably estimate population variability. This usually means a separate (but parallel) set of groups of animals in rodent studies. A single set of intravenous and oral dosing results from adult animals, when combined with some in vitro kinetic results, may provide an adequate data set for the design and interpretation of short-term, subchronic and chronic toxicity studies. 

To represent the POs for a vibronically coupled system in a intuitively clear way, we consider the classical electronic population variable A dia =... 

Perhaps there are some members of the human population under assessment (a subpopulation, such as children, women of child-bearing age, people with compromised immune systems, etc.) whose response to a given dose falls well outside the normal range of population variability. How can their risks be assessed ... 

From the formula for a confidence interval, its width is determined by three parameters the sample size, population variability and the degree of confidence. Plainly, if the sample size is increased then we have seen the standard error will be reduced and hence the width of the interval will also be reduced. If we can reduce the variability of the characteristic being studied then... 

An estimate of the population variability may be obtained from a pilot study, a literature metaanalysis (see Section 8.6) or phase 1/11 studies. 

Include in utero exposures and young children in biomonitoring designs because they are a substantial source of population variability in exposure and susceptibility. 

In addition, existing databases where environmental media and biomonitoring data are collected (such as NHEXAS) could be further studied to estimate exposure and explore the relationships between biomarker concentration and exposure. That information can be used to apportion chemical intake into the different exposure pathways to assist in interpreting population variability, to calculate exposure by combining environmental measurements with survey information to verify estimates of exposure from pharmacokinetic models, and to identify research needs on the basis of discrepancies between estimates obtained from the exposure-pathways analysis and biomonitoring results. 

The committee recommends that efforts be made to develop human pharmacokinetic models early in the study-design process to understand the influence of such factors as metabolism, sampling time, and population variability, that are critical to interpretation of the biomonitoring data. 

They have a much more powerful effect on data relevancy and validity than errors originating from sample or population variability. In fact, a thoughtfully conducted planning process takes into account the population variability at the project site, and errors originating from sample variability are controlled by the proper implementation of the field sampling procedures. 

Precision Error from sample variability Error from population variability Measurement error Field and laboratory procedure error... 

Boyce M. 1992. Population variability analysis. Annu Rev Ecol Syst 23 481-506. 

Incorporating Information on Population Variability into Mechanistic DM-PK-PD Modeling to Assess the Power of Pharmacogenetic Studies... 

Population variability The concept of differences in susceptibility of individuals within a population to drugs or toxicants due to genetic variations in metabolism, for example, or differences in biological responses. 

Stebbins, G. L., Self-Fertilization and Population Variability in the Higher... 

They provide the weighting factors for combining the derivatives with respect to the electron-population variables. For example, for the global chemical potential one obtains ... 

In terms of the CT-projected population variables, the hardness tensor is given by the diagonal matrix ... 

The transformation c can be partitioned into the matrix c, grouping the first (m — 1) columns and representing independent internal charge redistribution modes, and the last column, representing the pure CT displacement c = (c, c m). The (m — 1) collective populational variables,... 

The sample of individuals is assumed to represent the patient population at large, sharing the same pathophysiological and pharmacokinetic-dynamic parameter distributions. The individual parameter 0 is assumed to arise from some multivariate probability distribution 0 / (T), where jk is the vector of so-called hyperparameters or population characteristics. In the mixed-effects formulation, the collection of jk is composed of population typical values (generally the mean vector) and of population variability values (generally the variance-covariance matrix). Mean and variance characterize the location and dispersion of the probability distribution of 0 in statistical terms. 

Actively encourage exploration of the scope for increased crossover and better inclusion of the real-world issues of population variability and uncertainty. 

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