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PubMed2006

The impact of stigma, experience, and group referent on HIV risk assessments and HIV testing intentions in Namibia.

People often perceive risks for others and themselves differently. This study examines whether personal beliefs about HIV and experience with those living with HIV influence personal risk assessments of contracting HIV in an interview sample of northern Namibians (N=400), but not others' assessments as explained by singular-distribution theory [Klar, Medding, & Sarel (1996). Nonunique invulnerability: Singular versus distributional probabilities and unrealistic optimism in comparative risk judgments. Organizational Behavior and Human Decision Processes, 67, 229-245]. Findings indicate that personal risk perceptions decrease with more HIV stigmatizing beliefs and increase with greater experience, but that those characteristics had no impact on assessments for others' risk. The study also examines whether the size and characteristics of the referent group, peers and the general Namibian population, influence others' risk assessments. Optimistic biases for personal risk versus others' risk appear with the highest discrepancy emerging between personal and general population risk assessments. Further, we found that personal risk perceptions did not mediate the relationship between personal characteristics, beliefs and experiences, and intentions to seek HIV testing.

AIDS Serodiagnosis↗
PubMed1997

Information theoretical concepts in clinical chemistry: the use of spreadsheet programs for convenient calculation of information theoretical quantities.

Information theoretical concepts can be used as most valuable tools for evaluating clinical chemical tests. They offer several advantages over the conventional test evaluation by Bayesian concepts. Although long known, information theory has failed to gain widespread acceptance among clinical chemists, probably due to the rather laborious computation of the necessary quantities. To resolve this technical problem, this paper demonstrates how commonly available computer spreadsheet programs can assist in the computation of information theoretical quantities such as the diverse entropies and the information content. Two spreadsheet versions are presented: firstly, a working sheet is developed for information theoretical evaluation of a two-by-two contingency table corresponding to a dichotomous diagnostic problem (e.g., diseased versus non-diseased) and a dichotomous diagnostic test outcome (e.g., normal versus abnormal), and secondly, a working sheet is shown for a more general situation with up to ten diagnostic alternatives and up to ten possible test outcomes. Typical examples for application of these tools are demonstrated.

Chemistry, Clinical↗
PubMed1998

Time course of enzyme induction in humans: effect of pentobarbital on nortriptyline metabolism.

To study the effect of induction we gave six male volunteers 10 mg nortriptyline three times a day for 4 weeks and 0.2 gm pentobarbital on days 8 to 21. Plasma and urinary levels of nortriptyline and metabolites were measured. The rate and extent of induction of the enzyme(s) were estimated by a model with use of nortriptyline concentrations. There was a marked decrease of nortriptyline levels after 2 days of pentobarbital treatment. Total clearance of nortriptyline increased more than twofold (range, 1.6-fold to 4.1-fold). Apparent metabolic clearance by 10-hydroxylation increased markedly. The decrease in nortriptyline levels was more rapid than the increase after pentobarbital cessation, fitting with the theory of the model. The induction of nortriptyline metabolism is probably mainly the result of an increase in a non-CYP 2D6 P450 isozyme, possibly CYP 3A4 or a CYP 2C form. More knowledge of induction characteristics of drugs should lead to better predictions of decreased effects and appearance of adverse effects. The kinetic model used for analysis of our data could then be useful.

Adrenergic Uptake Inhibitors↗
PubMed2003

[A critical review of the pragmatic clinical trial].

Schwartz and Lellouch proposed in 1967 to differentiate between pragmatic and explanatory clinical trials. The pragmatic approach has been understood in different ways and has also been the object of some criticism. Yet different authors have asked to perform pragmatic clinical trials, especially in issues requiring a therapeutical decision. In order to clarify the present situation of the pragmatic trial, a bibliographic review has been performed. Between 1976 and 2002, 95 original articles on clinical trials conducted following a pragmatic design have been found. Only four followed strictly the approach developed by Schwartz et al. In a pragmatic clinical trial, it is usually not possible to blind the interventions and for this reason randomization is imperfect. This limitation casts doubts about the validity of the frequentistic methods in the intention-to-treat evaluation of the results of a pragmatic trial. This experimental approach demands an evaluation according to the decision-making theory. Following the Bayes theorem, the credibility and the previous probability of a hypothesis conditions its posterior probability. It has been agreed that Bayesian statistics is a suitable instrument for the evaluation of a pragmatic clinical trial, but the lack of adequate informatics' programs has limited seriously its application. Recently,some new programs (WinBUGS, TreeAge) have been developed and applied to the decision analysis in some primary care therapeutic questions. It seems possible to predict that, thanks to the new informatics'programs on Bayesian statistics, the pragmatic clinical trial will experience, in the short term, an important revival.

Bayes Theorem↗
PubMed1999

Self-restoration of biocomponents as a mean to enhance Biological Life Support Systems reliability.

One of the key problems of long-term space missions is limited service life of units. The only exceptions are biological components of biological Life Support Systems--higher plants or microorganisms. These components are capable of self-restoration: after complete disintegration, they can appear again from seeds or spores. The estimate of failure intensity of BLSS regeneration component includes: a number of self-sustained sections of the regeneration component; permissible boost (how many times can productivity of a component be increased); time required to repair (restore) a component; the crew existence time, when all LSS regeneration components fail; failure rate of one section of a regeneration component. Evaluations show that for hydrogen-oxidizing bacteria and micro-algae very high reliability is achieved even for one or two sections. In the case of higher plants (due to low rate of self-restoration) bio-regenerative module has to be divided into 10 self-sustained sections operating simultaneously. These measures can decrease the probability of catastrophe by a factor of 10(6).

Ecological Systems, Closed↗
PubMed2001

Hierarchical arrangement of psychiatric symptoms in the context of schizophrenia.

Foulds' model proposing a four-class hierarchical structure of mental illness represents an interesting dimension of psychiatric research and discussion and probably has a significant potential on diagnosis, taxonomy, therapeutics and theory. Psychiatric symptoms were investigated in a group of 244 schizophrenic patients with the purpose of analyzing Foulds and Bedford's notion that psychiatric symptoms are arranged hierarchically. To achieve this the R (recent) version of the Delusions, Symptoms, States, Inventory (DSSI) was administered in the form of a constructed interview to these patients. The hierarchical arrangement of psychiatric symptoms was verified since a great majority of the cases (80.8%) produced symptom patterns conforming to the hierarchy model. However, patients with duration of illness longer than 10 years reported conforming patterns in a lower percentage (77%), whereas 84.6% of those with a duration of illness less than 2 years reported conforming patterns. The non-conforming patterns were those in which integrated delusions were absent in the presence of delusions of disintegration, neurotic symptoms were absent in the presence of integrated delusions, and dysthymic states were absent in the presence of neurotic symptoms.

Adolescent↗
PubMed2003

Fuzzy epidemics.

The purpose of this paper is to provide a review of the current state of fuzzy logic theory in epidemiology, which is a recent area of research. We present four applications of fuzzy logic theory in epidemic problems, using linguistic fuzzy models, possibility measure, probability of fuzzy events and fuzzy decision making techniques. The results demonstrate that the applications of fuzzy sets in epidemiology is a very promising area of research. The final discussion sets the future stage of fuzzy sets application in epidemiology.

Acquired Immunodeficiency Syndrome↗
PubMed2006

Is the mechanism of the [2+2] cycloaddition of cyclopentyne to ethylene concerted or biradical? A completely renormalized coupled cluster study.

The mechanism of the [2+2] cycloaddition reaction of cyclopentyne to ethylene has been studied using the completely renormalized coupled cluster method with singles, doubles, and noniterative triples (CR-CCSD(T)). In agreement with the experimentally observed stereochemistry, the CR-CCSD(T) method favors the concerted pathway involving a [2+1] transition state, whereas the popular CCSD(T) method, which is often regarded as the "gold standard" of electronic structure theory, and low-order multireference methods support the less probable biradical mechanism. In addition, the CCSD(T) approach produces an erroneous description of some transition states and intermediates, particularly those which have a significant biradical character. The CR-CCSD(T) calculations indicate that the reaction is a highly exothermic (deltaG(r)298 = -68 kcal/mol), predominantly concerted process with a relatively low activation barrier on the order of 13-16 kcal/mol which permits its thermal occurrence.

Journal Article↗
PubMed1997

Interaction of light and gravitropism with nutation of hypocotyls of Arabidopsis thaliana seedlings.

Etiolated seedlings of Arabidopsis thaliana nutated under conditions of physiological darkness while about ten percent of monitored individuals exhibited regular elliptical nutation, circumnutation. Pre-irradiation with red light prevented occurrence of circumnutation without having an effect on the average rate of the nutational movement. Phototropic response of seedlings to unilateral blue light appeared to be superimposed over nutation. Throughout gravitropism, some seedlings continued to exhibit nutation suggesting that these two processes are independently controlled. Based on these results, we suggest that nutation in Arabidopsis probably is not controlled by the mechanism predicted by the theory of gravitropic overshoots.

Arabidopsis↗
PubMed1998

The transformation of the probability of a heart fatality into a queue position.

The population of Bury and Rochdale has a much higher rate of Coronary Heart Disease than the national average. This paper develops an approach, based on the Framingham score method, of making patients aware in a lucid manner of their risk of suffering a fatal heart attack by assigning them a position in a queue of people who are similar to them so far as non-modifiable risk factors are concerned.

Adult↗
PubMedDate not supplied

Valuing biodiversity: reality or mirage?

The objective of this paper was to consider the social value of biological diversity and explore if this value could be expressed in terms of a unidimensional metric in money. Economics distinguishes between use-values and non-use-values, which are critically evaluated for valuing biodiversity. It is shown that these utility-based valuations have severe limitations as they treat species in isolation from their ecological contexts. In contrast, ecosystem ecology regards ecosystems as an integrated non-linear and nonconvex system in which ecosystem functions can be understood as a four-component cycle; exploitation, accumulation of biomass, creative destruction and renewal. Within such a cycle, ecosystems can be seen to have two properties: stability and resilience. A good proxy for resilience is the probability of extinction of species, and social value of biodiversity can be expressed as a partial ordering with this probability as an index. This approach is consistent with decision theory, of which social choice is an important component, pioneered by Arrow.

Animals↗
PubMed1991

Worry is reasonable: the role of explanations in pessimism about future personal events.

This experiment examines one component of worry, elevated subjective probabilities of negative events, and attempts to elucidate the cognitive processes on which this is based. The results suggest that the pessimistic subjective probabilities shown by chronic worriers can be understood using general theories of judgment, specifically, by the use of the availability heuristic (Tversky & Kahneman, 1973). However, it is the availability of a particular pattern of cognitions--an increased accessibility of explanations for why a negative event would occur, combined with a reduced accessibility of explanations for why it would not--that is important. The results are integrated within a description of the worry process, and possible clinical applications through the use of reason-generation techniques are discussed.

Adult↗
PubMed1994

Retrieving information from memory: spreading-activation theories versus compound-cue theories.

McNamara (1992a) attacked compound-cue theories on a number of grounds. Using free association as a measure of distance between concepts in memory, he argued that compound-cue theories cannot explain mediated priming effects. The authors show that free-association production probabilities do not accurately predict priming effects, either directly or in the context of current spreading-activation models, and so remove the basis for McNamara's criticism. McNamara also claimed that compound-cue theories cannot account for the sequential effects of items that precede a target on responses to the target, but the authors show that sequential effects are consistent with compound-cue models if the target item is weighted more heavily than preceding items in the calculation of familiarity that determines response time and accuracy for the target. It is concluded that, although compound-cue and spreading-activation theories are both consistent with available data, the compound-cue theory, having less freedom, has passed more stringent tests.

Attention↗
PubMed2003

Context effects: the proportional difference model and the reflection of preference.

The reflection effect (D. Kahneman & A. Tversky, 1979) was investigated using the stochastic model of choice developed by C. Gonzalez-Vallejo (2002). The model assumes that individuals make trade-offs among attribute values by relying on a difference variable. The model also specifies a threshold representing individual proclivities to reach to attribute differences. Two experiments demonstrated that changes in risk attitudes, from a gain to a loss situation, depended on the stimuli as well as on individuals' thresholds. Thresholds were generally lower in losses than in gains, indicating a risk-taking tendency. Thresholds were also lower when participants were endowed with greater savings. Model testing revealed better fits for the stochastic model than cumulative prospect theory (A. Tversky &. D. Kahneman, 1992).

Choice Behavior↗