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At least 451 records · Page 25Linked to original sources
PubMed1993

A fractal model of HIV transmission on complex sociogeographic networks: towards analysis of large data sets.

"A paradigm of HIV (human immunodeficiency virus) transmission along very large 'sociogeographic' networks--spatially focused nets of social interaction--is extended to include fractal (dilationally self-similar) structures upon which a metric of 'sociogeographic' distance can be defined.... Techniques are sketched for determining the sociogeographic structure of a large, geographically centered social network, providing a possible empirical basis for predicting forms and rates of spread of the initial, rapid stages of an HIV outbreak for networks not yet infected, and perhaps greatly expanding the utility of routinely collected small-area administrative data sets in the design of mutually reinforcing, multifactorial disease-control strategies."

Communicable Diseases↗
PubMed1996

Randomized clinical trial of the efficacy and safety of a home bleaching procedure.

The safety and efficacy of a home-use carbamide peroxide tooth-whitening procedure were evaluated in a double-blind experimental design. Fifty-two adults were randomly assigned to experimental and control (placebo gel) groups. The products were applied in a custom-fitted tray and used for 5 consecutive nights in accordance with the manufacturer's recommendations. Tooth color changes from baseline were measured with a small-area colorimeter. Concurrently, electric pulp test and periodontal indices were measured. At the end of 6 months, the teeth in the active group had a statistically significant greater mean color change that did the placebo controls. The mean color change differed significantly by tooth type. No statistically significant changes in vitality, sulcus depth, or Gingival Index were found in the treatment group.

Adult↗
PubMedDate not supplied

Color perception among different dental personnel.

This study investigated the differences in color perception among distinct groups of dental personnel. Four groups of dental personnel (10 dental technicians, 15 final-year dental students, 15 general practitioners and 10 prosthodontists) were asked to match seven test tabs of shades A1, A4, B2, B3, C2, C4 and D3 (Z100 shade guide, 3M Dental Products, St Paul, MN 55144, USA) against a standard Vita shade guide under similar lighting conditions. The results obtained were computed into L*a*b* values using a small-area colorimeter (Dental Colorimeter, Minolta Camera Pte Ltd). The data were analyzed using one-way ANOVA/post-hoc Scheffe's test at significant level p<0.05. The results showed significant differences in deltaE (color difference) between the dental technicians and the clinicians for shade C4. The significant difference that was observed in deltaE for dark shades between dental personnel was mainly contributed to a disparity in L* values. A significant difference in deltaL* was observed between dental technicians and prosthodontists for shade C4.

Analysis of Variance↗
PubMedDate not supplied

Colorimetric evaluation of vita shade resin composites.

The shades of several resin composite materials are keyed to the Vita Lumin shade guide. This study was designed to determine whether different composites of the same designated Vita shade were actually similar in color. A small-area colorimeter was used to compare the L*a*b* color parameters of three hybrid resin composites--Pertac-Hybrid, Prisma AP.H, and XRV Herculite. Four Vita shades (A2, B3, C2, and D3) of each material were evaluated. Color differences (delta E values) between composites of the same designated shade ranged from 2.07 for the A2 shades of Herculite and AP.H to 7.64 for the D3 shades of Herculite and Pertac. Color differences in this range are perceptible to many observers under ideal viewing conditions.

Analysis of Variance↗
PubMed1998

Multi-drug resistant tuberculosis in Finland--a forecast.

Since the collapse of the Soviet system, travel between the St Petersburg district and the Baltic states and Finland has increased substantially. Although it is difficult to obtain exact figures on the number of cases of tuberculosis (TB) and multi-drug resistant (MDR) TB in these countries, there is strong evidence of growing epidemics, bringing added epidemiological threat to Finland. The purpose of this study is to produce a short-term "worst case" forecast of the spatial development of a threatened MDR-TB epidemic in Finland. The method applied is a chorological multistep procedure using statistical and geographical methods and a simulation technique. Instead of focusing on populations of carriers and susceptibles, emphasis is placed on identifying the primary influences directing the epidemic as a spatial process. This was done by dividing Finland into small-area units and by assigning the risk of obtaining MDR-TB to each unit based on socioeconomic and structural characteristics of the population. The simulated 6 year cumulative distribution of new MDR-TB cases showed a marked concentration of cases in the capital region and in a cluster of municipalities along the west coast. Although socioeconomic factors are important in explaining the distribution of cases, frequent and widespread international contacts seemed to be equally important at the beginning of the epidemic.

Disease Outbreaks↗
PubMed1995

Tooth color and reflectance as related to light scattering and enamel hardness.

Tooth color is determined by the paths of light inside the tooth and absorption along these paths. This paper tests the hypothesis that, since the paths are determined by scattering, a relation between color and scattering coefficients exists. One hundred and two extracted incisors were fixed in formalin, mounted in a standardized position in brass holders, and pumiced. A facet was prepared near the incisal edge on the labial plane to allow for Knoop hardness measurements with a 500-gram load. Light scattering by the enamel was measured in a 45 degrees/0 degrees geometry; light scattering by both enamel and dentin was measured in a 0 degrees/0 degrees geometry. The reflection spectrum of the tooth was measured from the labial plane with a spectroradiometer in a 45 degrees/0 degrees geometry, with standard illuminant A and standard illuminant D65. To include all volume-reflected light, we used entire-tooth illumination and small-area measurement. CIELAB color coordinates were calculated from the spectra. Neither spectra nor coordinates showed evidence of a contribution of fluorescence to tooth color. Averaged values and standard deviations for L*,a*,b* were 69.9 (4.1), 1.22 (1.4), and 17.9 (2.9), respectively. Both scattering coefficients averaged to 0.6 (0.4) mm-1; Knoop hardness number was, on average, 271 (39) kg/mm2. L* correlated with a* (r = -0.51), with the enamel scattering coefficient (r = 0.60), and slightly with hardness (r = 0.17, p = 0.03). The colors of 28 teeth from which the enamel was removed correlated strongly with the colors of the complete tooth.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemical Phenomena↗
PubMed2001

Impact of normative feedback on problem drinkers: a small-area population study.

OBJECTIVE: As many as one in four adults in North America experiences some problems due to alcohol consumption. Although most of these problem drinkers do not have concerns that are severe enough to merit formal treatment, such drinking has large economic costs and can place the drinker at risk for long-term negative health and social consequences. The present study evaluated a minimal intervention that used normative feedback about population drinking to motivate changes in alcohol use. METHOD: An intervention pamphlet was mailed to over 6,000 households in Toronto, randomized by block from a region containing almost 10,000 households. In the month after the mailing, a general population survey was conducted in the region to assess alcohol use. RESULTS: Respondents from households receiving normative feedback (n = 472) reported significantly lower alcohol use than controls (n = 225), but this effect occurred only among respondents who met an objective criterion for problem drinking and who perceived some risk associated with their drinking. CONCLUSIONS: Viewed from a public health perspective, normative feedback interventions have the potential for a significant payoff because they can be provided at low cost and to problem drinkers who might ordinarily never access any treatment services.

Adult↗
PubMed1997

Clustering of childhood IDDM. Links with age and place of residence.

OBJECTIVE: To improve understanding of the etiology of IDDM by analyzing spatial and space-time distribution of the incidence in children. RESEARCH DESIGN AND METHODS: Statistical tests to detect clustering were applied to a population-based register of 1,490 children (aged 0-16 years) with IDDM in Yorkshire, northern England. The Knox test analyzed clustering in space and time, and the Potthoff-Whittinghill test quantified spatial differences in incidence between small-area census units (electoral wards). The Potthoff-Whittinghill test was conditioned for childhood population density and deprivation (Townsend index). RESULTS: Both tests demonstrated clustering of IDDM in Yorkshire children. Space-time and spatial clustering is strongest in the younger children (0-4 and 5-9 years of age), even after conditioning for known associations. Clustering was more common in the county of Humberside during the years 1982-1985 and in wards of low population density (< 0.26 0- to 16 year-old subjects per hectare). CONCLUSIONS: The study revealed a nonrandom space-time distribution of IDDM in children not accounted for by known covarying demographic factors. The Potthoff-Whittinghill test has not previously been applied to childhood IDDM. The new finding of strong clustering in young children is consistent with early exposure, possibly in utero, to infectious agents or localized environmental sources.

Adolescent↗
PubMed1990

The uses and users of population projections in Australia.

"It is widely recognized that population projections are increasingly used in formulating policy in many public and private sectors. However, little information exists on the nature of the projections or their users. This paper reports the results of a survey conducted to rectify this situation. The results confirm that the applications of projections are very broad and that the prime area of increase has been in small-area projections. At this level many users make their own projections rather than use official projections and the paper reviews the methodology used to make these projections. A number of suggestions are made for improving communication between national and subnational producers and local users." The geographical focus is on Australia.

Australia↗
PubMed1993

Variation in hysterectomy rates across small geographic areas of Massachusetts.

OBJECTIVE: Our objective was to determine whether small-area variation in hysterectomy rates exists within Massachusetts and, if so, whether regions with persistently high or low rates can be identified. STUDY DESIGN: By examining data derived from standardized hospital discharge forms between 1982 and 1989, we compared hysterectomy rates among 172 small geographic areas within Massachusetts. The ratios of actual to expected number of hysterectomies for each area were also computed. Statistical significance of rate variation was established by a value of p < 0.01 (chi 3 test). RESULTS: The-hysterectomy rate per 1000 women varies fivefold across small-population areas of Massachusetts. Eight areas had persistently high and five had persistently low rates compared with the statewide average. CONCLUSION: Possible explanations for these rate variations include indigenous population factors, supply of health care resources, income, insurance coverage, methodological problems in data analysis, and variation in professional judgment with regard to the indication for hysterectomy. Only a combination of the study of local causes of high and low rates and the study of the clinical outcomes of different treatment decisions will allow physicians to develop an informed consensus on appropriate indications for surgery.

Female↗
PubMed1988

Display of small-area variation in health-related data: a methodology using resistant statistics.

Health care planning requires characterization of the population to be served. Examination of available demographic and epidemiologic data is one early step in this process. However, aggregate data for the entire geographic area of concern often fail to reveal important differences among geographically defined sub-populations--differences that influence the form an effective delivery system should take. We present a methodology based on exploratory data analysis (EDA) techniques that we have found useful in examining health-related data for our ambulatory care catchment area. Our examples use three population characteristics that have major implications for health care planning for the elderly: 1970-1980 change in population aged 65+; the percent of the population aged 65+ below poverty level; and the percent of single-person households among households with one or more persons aged 65+. With these data for the 25 municipalities of Middlesex County, New Jersey, we illustrate a two-step process: (1) the construction of stem-and-leaf displays that permit examination of a data distribution for asymmetry, concentrations around specific values, gaps in values, and outliers; and (2) the use of the median, the fourth-spread, and other information from the stem-and-leaf display in the systematic selection of data value classes to be given distinct shadings on a map of the selected geographic area. Discussion emphasizes the usefulness of graphic display of data in detecting similarities and unusual data values. Comparison of maps based on the EDA techniques and maps based on several traditional methods of value classing for the same data illustrates the influence of classing choices on the interpretation of cartographic displays of health-related data.

Aged↗
PubMed1998

Nitrate in drinking water and the incidence of gastric, esophageal, and brain cancer in Yorkshire, England.

OBJECTIVES: This small-area ecologic study in Yorkshire, northern England, examines the hypothesis that exposure to higher levels of nitrate in drinking water increases the risk of stomach, esophageal, or brain cancer in adults. METHODS: Nitrate levels over the period 1990-95 and numbers of incident cancers from 1975-94 were available for 148 water supply zones, geographically defined areas each supplying water of homogeneous chemical composition to an average population of around 20,000. RESULTS: No relationship was found between nitrate concentrations and the incidence of stomach or esophageal cancers. The incidence of cancer of the brain and central nervous system was found to be higher in areas with higher nitrate levels, with a relative risk of 1.18 (95 percent confidence interval = 1.08-1.30) in the quartile of the population with the highest average levels (mean 29.8 mg/l) compared with the lowest quartile (mean 2.4 mg/l). The increase in risk remained statistically significant (P < 0.01) after allowing for other covariates and for extra-Poisson variation in a regression model. CONCLUSIONS: This study does not support the hypothesis of an increased risk of stomach or esophageal cancer associated with higher nitrate levels in drinking water. The observed relationship with brain cancer requires confirmation in other studies, including those involving data on individuals.

Adolescent↗
PubMed1998

The estimation of population microdata by using data from small area statistics and samples of anonymised records.

"Traditionally, estimates of the number of people in small areas (the smallest geographical units for which data are available) have been disaggregated only by age and sex. More recently, much research effort has been directed towards developing some form of enhanced small-area population estimation, in which the population in a small area is disaggregated not only by age and sex, but also by a wide range of additional economic and social characteristics. Solutions to this problem currently include account-based demographic models, often used by local authorities."

Age Factors↗
PubMed1990

Geographic variations in US asthma mortality: small-area analyses of excess mortality, 1981-1985.

US asthma mortality rates have been increasing during the past 10 years. Little is known about the geographic variation of this infrequent health event. Using US vital records for the 1981-1985 period, small-area variation of excess asthma mortality of young adults was studied. Several geopolitical definitions were used to define populations. A total of 22 single counties, 12 metropolitan statistical areas, 11 health service areas, and 29 state economic areas were identified as having mortality significantly in excess of that expected, based on US race/sex-specific rates. Significant variation in asthma mortality was found at several levels of geopolitical classification of the data. Elevated areas included the central plains states and three large urban metropolitan areas--Chicago, Illinois, New York, New York, and Phoenix, Arizona--as well as a few mostly suburban populations. Areas with excess mortality may provide a useful population base for further epidemiologic investigation into the risk factors associated with the more frequent morbid events of this disease, such as emergency room and hospital utilization.

Adolescent↗
PubMed1999

Risk of low birthweight in social districts of Copenhagen.

The purpose of this survey was to investigate the small-area variations in low birthweight within social services districts in Copenhagen and the relation of such variations to the socioeconomic characteristics of the district. The study was based on register data and included all live-born single on births to women living in the city of Copenhagen from 1987-90. We found a statistically significant association between district and risk of newborns being small-for-gestational age (SGA). This association was independent of adjustment for maternal age and parity. Only part of the association was explained, though this was still significant, using an index summarizing the socioeconomic living conditions in the district. Splitting up the index into its four constituent components, however, showed that the association between SGA and district was primarily due to housing conditions in the districts. Mapping the districts demonstrated a clear tendency of clustering of the high-risk areas with poor socioeconomic conditions.

Cluster Analysis↗
PubMed1994

Estimating temporary populations.

The difficulty of tracking temporary short-term population movements (commuting, seasonal visitation, convention and business travel) is examined, with a focus on Hawaiian statistician Robert Schmitt's work. The author finds that "Schmitt's contributions toward a methodology for estimating daytime populations were important because this approach utilized data sources that were widely available for small areas on at least an annual basis. Consequently, this approach could be used for frequent updates of the estimates, for many areas and at relatively little cost.... The major drawback of the approach is the lack of solid data on temporary residents to serve as larger-area control totals and as a historical base for small-area estimates." The geographical focus is on the United States, particularly Hawaii.

Americas↗