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Results for “environmental variability”

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At least 163 records · Page 9Linked to original sources
PubMed1984

Relationship between physical, psychological, social, and environmental variables and subjective sleep quality.

In a survey study of patients of a general practitioner the relationship between sleep quality and a heterogeneous set of other variables was examined. The data file was divided randomly, and a two-staged multiple regression analysis was performed on each half. The two resulting regression equations were cross-validated on the data of the other data file. The variables mood, age, and use of medicine proved to have the most significant relationship to sleep quality.

Adult↗
PubMed1994

Influence of demographic, socioeconomic and environmental variables on childhood diarrhoea in a rural area of Zaire.

There have been very few longitudinal studies of diarrhoea morbidity in sub-Saharan Africa. This longitudinal study of children aged 3-35 months from 18 clusters of villages reports an annual incidence rate of 6.3 episodes per child in a rural area of Zaire, which is higher than a cross-sectional estimate previously obtained in the same district. The study confirms that a child's risk of diarrhoeal attack is associated with age, water quality and sanitation, parental education and household size. The findings suggest also that birth interval may be an important risk factor for diarrhoeal morbidity.

Age Factors↗
PubMed1996

Environmental variables and mobility performance in adults with low vision.

BACKGROUND: Surveys and empirical studies of visually impaired (VI) persons suggest that avoidance of objects while walking may depend on type of vision loss and be influenced by light level, object contrast, and object type. METHODS: Mobility performance in 88 VI adults was assessed on an indoor obstacle course under photopic and mesopic lighting conditions. Subjects were divided into three categories: primarily an acuity loss, primarily a peripheral field restriction, and a combination of the two. Performance measures were time to walk the course and total number of contacts with objects in the course. RESULTS: Decreasing light level from photopic to mesopic resulted in a significant increase (roughly double) in the time required to complete the course and in the total number of contacts, regardless of type of vision loss. Under photopic illumination, subjects with acuity loss took less time on average to complete the course and contacted fewer objects than the other two groups. At mesopic levels, acuity loss subjects performed better than those in the other categories. Low contrast obstacles were contacted more frequently than high contrast ones at both light levels. Finally, floor level walk-around objects were contacted significantly less often than either step-over or head level objects, regardless of type of vision loss and light level. CONCLUSIONS: The ability of VI persons to avoid obstacles is significantly impaired under mesopic illumination. Object contrast and location are significant factors in determining the success of VI persons in avoiding obstacles in the travel path.

Adult↗
PubMed1998

Spatial analysis of lymphatic filariasis distribution in the Nile Delta in relation to some environmental variables using geographic information system technology.

Geographic information system (GIS) was used to analyze the spatial distribution of filariasis in the Nile Delta. The study involved 201 villages belonging to Giza, Qalubiya, Monoufiya, Gharbiya, and Dakahliya governorates. Villages with similar microfilarial (mf) prevalence rates were observed to cluster within 1-2 km distance, then, clustering started to decrease significantly with distance up to 5 km (Pearson correlation coefficient = -0.98). the likelihood of negative and high prevalence villages being contiguous was very low (approximately 1.8%, n = 612 village-pairs) indicating homogeneity in disease processes within the defined spatial scales. Of the villages located within 2 km from the main Nile branches (n = 46), 95% exhibited low prevalence. In addition, the spatial pattern of mf prevalence was shown to be negatively associated with annual rainfall and relative humidity, while it was positively associated with annual daily temperature. Average mf prevalence in warmer, relatively drier areas receiving 25 mm of rain was significantly higher (3.9%) than that in less warmer but more humid areas receiving 50 mm of rain (1.6%) (P < 0.0001). Based on the results of the present study, GIS was used to generate a "filariasis risk map" that could be used by health authorities to efficiently direct surveillance and control efforts. This investigation identified some of the factors underlying filariasis spatial pattern, quantified clustering and demonstrated the potential of GIS application in vector-borne disease epidemiology.

Animals↗
PubMedDate not supplied

[Bacteriological quality of Bendetti Lake (Santo Tomé, Santa Fe Province, Argentina) and associated environmental variables].

The main objective was to determine the bacteriological quality of a shallow lake in the lower Salado River Basin (Bedetti, 31 degrees 40' S and 60 degrees 45' W). Seventy samples were tested by the most probable number (MPN) method, throughout three years. The number of thermotolerant coliforms was very variable: from 20 MPN/100 ml to 130,000 MPN/100 ml. These variations were mainly associated to the local rains (rs = 0.4853, p = 0.0001) and to the hydrometric level-h-(rs = 0.3835, p = 0.008). Statistically significant correlations between coliform bacteria and other variables (temperature, oxygen, pH, conductivity and transparency) were not found. The increase of coliforms associated to the increase of the hydrometric level indicates the presence of diffuse contamination sources. It was found that the rains affected the bacteriological quality, specially during the low water periods (h < 3.60). During the high water periods (h > 4.70) one of the main coliform contributor was represented by the incoming floating islans and aquatic macrophyte, from allochthonous fluvial systems. The coliform concentrations between the Bedetti lake and the Salado river were compared. The results show a better bacteriological quality of the lake (geometric average = 1,990/100 ml vs. 420/100 ml, n = 56) so that, connecting them by the construction of an artificial channel is not advisable.

Argentina↗
PubMed2000

Environmental colour affects aspects of single-species population dynamics.

Single-species populations of ciliates (Colpidium and Paramecium) experienced constant temperature or white or reddened temperature fluctuations in aquatic microcosms in order to test three hypotheses about how environmental colour influences population dynamics. (i) Models predict that the colour of population dynamics is tinged by the colour of the environmental variability. However, environmental colour had no effect on the colour of population dynamics. All population dynamics in this experiment were reddened, regardless of environmental colour. (ii) Models predict that populations will track reddened environmental variability more closely than white environmental variability and that populations with a higher intrinsic growth rate (r) will track environmental variability more closely than populations with a low r. The experimental populations behaved as predicted. (iii) Models predict that population variability is determined by interaction between r and the environmental variability. The experimental populations behaved as predicted. These results show that (i) reddened population dynamics may need no special explanation, such as reddened environments, spatial subdivision or interspecific interactions, and (ii) and (iii) that population dynamics are sensitive to environmental colour, in agreement with population models. Correct specification of the colour of the environmental variability in models is required for accurate predictions. Further work is needed to study the effects of environmental colour on communities and ecosystems.

Animals↗
PubMed2004

Violent crime and outdoor physical activity among inner-city youth.

BACKGROUND: Previous studies have shown poor correlation between subjective assessments of neighborhood safety and physical activity. This study was performed to model relationships between adolescents' outdoor physical activity and objectively measured violent crime densities, along with other key environmental variables. METHODS: Participants' physical activity was measured using a validated questionnaire. Multiple regression analysis was performed using outdoor physical activity away from school (OPA) as the dependent variable. Environmental factors included the density of violent crime within 1/2 mi of each participant's home, distance to nearest open play space, per capita income, and participants' subjective assessment of neighborhood safety. RESULTS: Multiple regression analysis showed that distance to nearest open play space was inversely and significantly associated with boys' OPA, while density of violent crime within 1/2 mi of home was inversely and significantly associated with girls' OPA. Girls' perceptions that their neighborhood was safe for physical activity were also associated with higher levels of OPA, while boys' assessments of neighborhood safety were not significantly related to OPA. CONCLUSIONS: Neighborhood violent crime may be a significant environmental barrier to outdoor physical activity for urban dwelling Mexican-American adolescent girls. Future studies of physical activity and the environment should use objective measures of environmental factors.

Adolescent↗
PubMed2005

Linear parameter haplotype models with stratification.

OBJECTIVES: The question of interest is estimating the relationship between haplotypes and an outcome measure, based upon unphased genotypes. The outcome of interest might be predicting the presence of disease in a logistic model, predicting a numeric drug response in a linear model, or predicting survival time in a parametric survival model with censoring. Explanatory variables may include phased haplotype design variables, environmental variables, or interactions between them. METHODS: We extend existing generalized linear haplotype models to parametric survival outcomes. To improve the stability of model variance estimates, a profile likelihood solution is proposed. An adjustment for population stratification is also considered. Here we investigate data sampled from known 'strata' (e.g., gender or ethnicity) that influence haplotype prior probabilities and thus the regression model weights. Differing linear model variance estimates, and the effect of stratification and departures from Hardy-Weinberg Equilibrium (HWE) on parameter estimates, are compared and contrasted via simulation. RESULTS: From simulations, we observed an improvement in statistical power when using a solution to profile likelihood equations. We also saw that stratification had little impact on estimates. Haplotypes that are not in HWE had a negative impact on power to test hypotheses. Finally, profile likelihood solutions for haplotypes deviating from HWE had improved power and confidence interval coverage of regression model coefficients.

Carcinoma, Squamous Cell↗