Home About us Contact
|
Home About us Contact | ||
|
|
||
Uncontrolled Variables (uncontrolled + variable)
Selected AbstractsInvasion success: does size really matter?ECOLOGY LETTERS, Issue 2 2002A. W. Miller The recent paper by Roy et al. (2001) presents a compelling relationship between range limit shifts, climatic fluctuations, and body size for marine bivalves in the fossil record. However, their extension of body size as a correlate for contemporary marine bivalve introductions is problematic and requires further scrutiny. Unlike their analysis of the fossil assemblage, the approach used for contemporary invasions does not adequately control for dispersal mechanism (vector) or source region. First, their analysis included mariculture species, intentionally introduced because of their large size, creating a vector-specific bias. Second, successful invaders from multiple source regions (Northern Hemisphere) were compared with potential invaders from a single source region (north-eastern Pacific), leaving both source and vector as uncontrolled variables. We present an analysis of body size for bivalve introductions from a single vector and source region, indicating no correlation between body size and invasion success when eliminating intentional introduction, source region and transport vector as confounding factors. [source] Evaluating effectiveness of preoperative testing procedure: some notes on modelling strategies in multi-centre surveysJOURNAL OF EVALUATION IN CLINICAL PRACTICE, Issue 1 2008Dario Gregori PhD Abstract Rationale, In technology assessment in health-related fields the construction of a model for interpreting the economic implications of the introduction of a technology is only a part of the problem. The most important part is often the formulation of a model that can be used for selecting patients to submit to the new cost-saving procedure or medical strategy. The model is usually complicated by the fact that data are often non-homogeneous with respect to some uncontrolled variables and are correlated. The most typical example is the so-called hospital effect in multi-centre studies. Aims and objectives, We show the implications derived by different choices in modelling strategies when evaluating the usefulness of preoperative chest radiography, an exam performed before surgery, usually with the aim to detect unsuspected abnormalities that could influence the anaesthetic management and/or surgical plan. Method, We analyze the data from a multi-centre study including more than 7000 patients. We use about 6000 patients to fit regression models using both a population averaged and a subject-specific approach. We explore the limitations of these models when used for predictive purposes using a validation set of more than 1000 patients. Results, We show the importance of taking into account the heterogeneity among observations and the correlation structure of the data and propose an approach for integrating a population-averaged and subject specific approach into a single modeling strategy. We find that the hospital represents an important variable causing heterogeneity that influences the probability of a useful POCR. Conclusions, We find that starting with a marginal model, evaluating the shrinkage effect and eventually move to a more detailed model for the heterogeneity is preferable. This kind of flexible approach seems to be more informative at various phases of the model-building strategy. [source] Operational implications of varying ambient light levels and time-of-day effects on saccadic velocity and pupillary light reflexOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 2 2007Minzhong Yu Abstract Changes in maximal saccadic velocity (SV), initial pupil diameter (IPD), constriction latency (CL) and constriction amplitude (CA) determined by the pupillary light reflex have been found to be sensitive indicators of impairment as a result of drugs, sleepiness, and/or fatigue. Ambient illuminance and time of day are controlled when these indices are applied as repeated measures in fitness-for-duty determinations. The application of oculometrics in unrestricted operational environments, where ambient illuminance and time-of-day testing are not constant, requires understanding of, and potential compensation for, the effects of, and interactions among, these multiple uncontrolled variables. SV, IPD, CL, and CA were evaluated in the morning and evening on two consecutive days following adequate nightly sleep under one baseline ambient illuminance and seven test ambient illuminances. Sixteen healthy volunteers (21,38 years, eight females/eight males) participated. Within and across days, SV was unaffected by decreasing ambient light or time-of-day effects. With the increase of ambient light from 670 to 3300 lx, CL decreased by 1%, while IPD and CA decreased by 17% and 20%, respectively. IPD increased with time of day by 1,10% (IPD was smaller in the morning). The results show that SV and CL are essentially resistant to changes in ambient light and time-of-day effects, simplifying their application in uncontrolled operational environments. [source] Suicide risk during anticonvulsant treatment,PHARMACOEPIDEMIOLOGY AND DRUG SAFETY, Issue 5 2010Maurizio Pompili MD Abstract Recent research findings suggest possible increases in risk of suicidal behaviors among patients treated with anticonvulsants. The available evidence appears to support such a risk more clearly for patients diagnosed with epilepsy rather than with primary psychiatric disorders. However, the studies involved are limited by providing associational findings that may be confounded by several uncontrolled variables. Such limitations should be considered in future research on adverse effects of anticonvulsants and other centrally acting drugs. For now, however, clinical prudence calls for routine, ongoing assessment of mood and suicidal thoughts among neurological or psychiatric patients, whether or not treated with particular drugs. Copyright © 2010 John Wiley & Sons, Ltd. [source] | ||||||||||