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P Elliott

Publications and source records attributed to P Elliott.

At least 127 records · Page 7Linked to original sources
PubMed1995

A standardisation approach to the control of socioeconomic confounding in small area studies of environment and health.

OBJECTIVE: To assess how effectively a routine adjustment can be made for socio-economic confounding in small area studies of environment and health using indirect standardisation and small area deprivation indices, including analysis of the appropriate size of population unit on which to base the deprivation index and the importance of region and urban/rural status as axes of stratification. METHODS: Standardised morbidity ratios were calculated for cancers in Great Britain for 1981 and standardised mortality ratios for all cause mortality in Great Britain between 1982 and 1985. Deprivation indices were calculated for enumeration districts and wards from 1981 small area census statistics. Cancers and deaths were allocated to enumeration districts via their postcode. Standardised morbidity and mortality ratios were calculated by quintile of enumeration district according to the deprivation index. Standardised mortality ratios were further analysed by deprivation of ward, region, and urban/rural status. RESULTS: Strong relationships were found between all cause mortality and the incidence of selected cancers and deprivation quintile-there was up to a twofold difference in lung cancer incidence between the highest and lowest quintile. The deprivation index can be used to measure gradients of deprivation according to the distance from industrial sites. The deprivation index for enumeration districts showed similar discrimination of mortality as the index forwards. There is some interaction between deprivation and region in their effect on the standardised mortality ratios, leading to a small bias in the estimation of expected numbers if this is not taken into account. The relationship between deprivation, urban/rural status, and mortality is complex and confounded by region, but mortality tends to be higher in urban than in rural areas within quintiles of deprivation. DISCUSSION: Whether calculated for enumeration districts or wards, the main problems in the interpretation of the deprivation index may be its limited correlation with the risk factors of interest and its concentration on present rather than past socioeconomic status. Indirect standardisation based on stratification for deprivation and other variable involves a trade off between bias and precision in determining the fineness and the number of axes of stratification. Some bias may occur due to interaction between region and deprivation and the effects of urban/rural status. Complementary approaches including modeling and proportional mortality or morbidity analyses may be needed and the possibility of residual socioeconomic confounding must always be considered. CONCLUSION: There is potential for important socioeconomic confounding in small area studies of environmental pollution and health where the health outcome under examination has a strong relationship to socioeconomic status and where the putative excess risk due to pollution may be small. One method of controlling for confounding is to use an ecological measurement of deprivation in small areas, and to adjust for deprivation by indirect standardisation. However, residual socioeconomic confounding can be expected, which may seriously complicate the interpretation of small area studies.

Adolescent↗
PubMed1995

Investigation of disease risks in small areas.

The investigation of disease risks in small areas is complicated by many issues including data quality, the retrospective nature of the statistical testing, the problems of boundary definitions in time and space around a putative disease cluster, and the lack of generally accepted definitions of the key terminology. Routine data systems have revolutionised the initial investigation of disease risks near sources of environmental pollution, although problems of data analysis and interpretation remain. This is especially true of unmeasured socioeconomic confounding, which could generate apparent positive results near a pollution source.

Environmental Pollution↗
PubMed1995

Cancer incidence and mortality near the Baglan Bay petrochemical works, South Wales.

OBJECTIVES: To study incidence and mortality of leukaemias, cancer of the larynx, and other cancers near the petrochemical plant at Baglan Bay, in response to local concerns of an alleged cluster of cancers in the vicinity. METHODS: This is a small area study of cancer incidence, 1974-84 and of mortality, 1981-91 based on the national postcoded data held by the Small Area Health Statistics Unit and with population and socioeconomic data from the 1981 census. The study is centred on BP Chemicals Ltd, Baglan Bay, Port Talbot, West Glamorgan, South Wales and includes a general population sample of 115,721 people (1981 census) living within 7.5 km of the plant. Cancer incidence and mortality for all cancers, leukaemias, and cancer of the larynx were examined within 7.5 km and 3 km of the plant, and tests for decline in risk of these cancers with distance from the plant were carried out. Mortality from several other cancers possibly associated with the petrochemical industry was also studied. RESULTS: There were 5417 incident cancer cases and 2458 cancer deaths within 7.5 km of the plant during the periods of study. There was an 8% excess incidence of all cancers within 7.5 km, and a 24% excess of cancer of the larynx, consistent with a general excess of these cancers in West Glamorgan, but no apparent decline in incidence with distance from the plant, nor excess mortality. There was also no evidence of decline in leukaemia incidence or mortality with distance, at all ages or in children. Among the other causes included in the mortality study, there was an excess of multiple myeloma within 7.5 km, especially among women, and a significant decline in mortality from non-Hodgkin's lymphomas although there was no excess overall within 7.5 km. CONCLUSIONS: The apparent excess incidence of all cancers and cancer of the larynx within 7.5 km of the BP Chemical Ltd works was consistent with an excess more generally in West Glamorgan, possibly related, at least to some extent, to cancer registration in Wales. There was no excess mortality from these cancers. The results for multiple myeloma and especially non-Hodgkin's lymphomas may have been chance findings in view of the multiple tests of significance carried out in the study. A study of lymphatic and haematopoietic cancers near oil refineries in Great Britain is to be undertaken that will help put the findings of the present study in wider context.

Adolescent↗
PubMed1995

Spatial statistical methods in environmental epidemiology: a critique.

Despite recent advances in the available statistical methods for geographical analysis, there are many constraints to their application in environmental epidemiology. These include problems of data availability and quality, especially the lack in most situations of environmental exposure measurements. Methods for disease 'cluster' investigation, point source exposures, small-area disease mapping and ecological correlation studies are critically reviewed, with the emphasis on practical applications and epidemiological interpretation. It is shown that, unless dealing with rare diseases, high specificity exposures and high relative risks, cluster investigation is unlikely to be fruitful, and is often complicated by the post hoc nature of such studies. However, it is recognized that in these circumstances proper assessment of the available data is often required as part of the public health response. Newly available methods, particularly in Bayesian statistics, offer an appropriate framework for geographical analysis and disease mapping. Again, it is uncertain whether they will give important clues as to aetiology, although they do give valuable description. Perhaps the most satisfactory approach is to test a priori hypotheses using a geographical database, although problems of interpretation remain.

Adult↗
PubMed1995

Dietary calcium and blood pressure: a review of the observational studies.

The objective of this study was to assess whether the epidemiological data support a relation between dietary calcium intake and blood pressure (BP). Fifty three published reports of observational studies relating intake of calcium or calcium-rich foods to BP in the USA (n = 33), Canada (n = 3), Puerto Rico (n = 1), Europe (n = 9), Asia (n = 5), Australia (n = 1) and South Africa (n = 1) were identified including a Medline search (January 1983-November 1993). Sample size ranged from 55 to over 58,000 (median 885). Five studies were prospective, 48 cross-sectional, of which four also contained a longitudinal component. Various dietary methodologies were used; the most common was the 24 h dietary recall. Most studies controlled for age, sex and body mass index, with variable control for other confounders. Many reports also allowed identification of subgroups by sex, age and race. One hundred and eight population samples and subgroups could then be identified. There was inconsistency in results both within and between studies. In 12 of the 53 published reports simple regression coefficients were reported. Median regression coefficients were -0.033 mm Hg/100 mg Ca (range -4.90 to +/- 0.47; n = 12) for systolic blood pressure (SBP) and -0.140 mm Hg/100 mg Ca (range -9.40 to +1.63; n = 10) for diastolic blood pressure (DBP). The association between dietary calcium intake and BP could not be assessed in all 108 population samples and subgroups because of design features, incompleteness of reported results and methods of analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1995

The use of geographical information systems in studies on environment and health.

Geographical information systems (GIS) provide a powerful technology for the spatial analysis of environmental and health data. Major areas of application include the assessment and mapping of environmental exposure, mapping of health outcome, and the analysis of spatial relationships between environment and health. The use of GIS nevertheless brings with it many potential problems and pitfalls. This article reviews some of the recent applications in relation to studies of environment and health, and examines some of the research issues involved.

Bias↗
PubMed1994

Prenatal determination of fetal rhesus D status by DNA amplification of peripheral blood of rhesus-negative mothers.

We have developed a sensitive PCR-based assay for the RhD gene and used it to detect circulating fetal cells from RhD-positive fetuses from peripheral blood of RhD-negative mothers. With further improvement in diagnostic accuracy, this assay may have implications in the management of RhD-sensitized pregnancies in women whose partners are heterozygous for the RhD gene. Further studies are required to determine the relationship between maternal anti-D levels and circulating fetal cell numbers.

Amniotic Fluid↗
PubMed1994

Alcohol and blood pressure: the INTERSALT study.

OBJECTIVES: To assess the relation between alcohol intake and blood pressure in men and women and in men at younger and older ages; to examine the influence of amount and pattern of alcohol consumption, as well as of acute effects, taking into account body mass index, smoking, and urinary sodium and potassium excretion. DESIGN: Subjects reported alcohol consumption for each of seven days before standardised blood pressure measurement, and whether they had consumed any alcohol in the 24 hours before measurement. SETTING: 50 centres worldwide. SUBJECTS: 4844 men and 4837 women aged 20-59. MAIN OUTCOME MEASURES: Effect of alcohol on blood pressure estimated by taking a weighted average of regression coefficients from centres. Acute effect assessed by examining mean differences in blood pressure of non-drinkers and of heavy drinkers who had and had not consumed alcohol in the 24 hours before measurement. Effect of pattern of consumption assessed by examining mean differences in blood pressure of non-drinkers compared with drinkers (i) whose intake was concentrated in fewer days or who were drinking more frequently, and (ii) whose alcohol intake varied little over the seven days or varied more substantially, as indicated by the standard deviation of daily consumption. RESULTS: Of the 48 centres in which some people reported consuming at least 300 ml/week of alcohol, 35 had positive regression coefficients linking heavy alcohol consumption to blood pressure. Overall, alcohol consumption was associated with blood pressure, significantly at the highest intake. After account was taken of key confounders, men who drank 300-499 ml alcohol/week had systolic/diastolic blood pressure on average 2.7/1.6 mmHg higher than non-drinkers, and men who drank > or = 500 ml alcohol/week had pressures of 4.6/3.0 mmHg higher. For women, heavy drinkers (> or = 300 ml/week) had blood pressures higher by 3.9/3.1 mmHg than non-drinkers. Heavy drinking and blood pressure were strongly associated in both sexes, and in men at both younger (20-39 years) and older (40-59 years) ages. In men who were heavy drinkers, episodic drinkers (those with great variation in daily alcohol consumption) had greater differences in blood pressure compared with non-drinkers than did regular drinkers of relatively constant amounts. CONCLUSION: The significant relation of heavy drinking (3-4 or more drinks/day) to blood pressure, observed in both men and women, and in younger and older men, was independent of and added to the effect on blood pressure of body mass index and urinary excretion of sodium and potassium. The findings indicate the usefulness of targeting those at high risk as well as the general population to reduce the adverse effects of alcohol on blood pressure.

Adult↗
PubMed1994

Urinary electrolyte excretion in 24 hours and blood pressure in the INTERSALT Study. I. Estimates of reliability. The INTERSALT Cooperative Research Group.

This is the first of two reports dealing with the reliability of measurements of 24-hour urinary electrolyte excretion and blood pressure and estimates of electrolyte-blood pressure associations in INTERSALT, an international study of the relations of electrolyte excretion and other factors to blood pressure, involving more than 10,000 persons from 52 centers in 32 countries. This first report describes methods for estimating reliability, taking into account age and sex, and provides estimates for several urinary variables, blood pressure, and pulse rate. The second report (Am J Epidemiol 1994; 139:940-51) uses these estimates of reliability and multivariate procedures to correct multiple regression coefficients from regressions of blood pressure on 24-hour urinary sodium and potassium excretion, body mass index, and alcohol intake for "regression dilution bias." Age- and sex-adjusted estimates of reliability were computed from data on 805 INTERSALT participants with repeat measurements. These estimates ranged from 0.37 to 0.40 for 24-hour urinary sodium, from 0.47 to 0.52 for potassium, from 0.32 to 0.36 for the sodium:potassium ratio, from 0.64 to 0.69 for calcium, from 0.59 to 0.65 for creatinine, from 0.49 to 0.57 for urinary volume, from 0.49 to 0.51 for magnesium, from 0.58 to 0.62 for pulse, from 0.69 to 0.74 for systolic blood pressure, and from 0.63 to 0.67 for diastolic blood pressure. In addition, estimates of within- and between-person covariances among electrolytes indicated that about half of the observed covariance for sodium and potassium excretion in a single 24-hour urine collection was due to within-person covariation in excretion.

Adult↗
PubMed1994

Urinary electrolyte excretion in 24 hours and blood pressure in the INTERSALT Study. II. Estimates of electrolyte-blood pressure associations corrected for regression dilution bias. The INTERSALT Cooperative Research Group.

This is the second of two reports dealing with the reliability of measurements of 24-hour urinary electrolyte excretion and blood pressure and estimates of electrolyte-blood pressure associations in INTERSALT, an international study of the relations of electrolyte excretion and other factors to blood pressure, involving more than 10,000 persons from 52 centers in 32 countries. The first report (Am J Epidemiol 1994; 139:927-39) described methods of estimating reliability, taking into account age and sex, and provided estimates for several urinary variables, blood pressure, and pulse rate. This second report uses these estimates of reliability and multivariate procedures to correct associations with blood pressure for "regression dilution bias." In these analyses, the estimated mean change in systolic blood pressure associated with a 100-mmol decrease in sodium intake was -3.1 mmHg with adjustment for age, sex, body mass index, and alcohol intake. For potassium, the estimated mean change in systolic pressure associated with a 15-mmol increase in potassium intake was -1.0 mmHg. These estimates are 44%-50% larger than those previously reported in INTERSALT, based on simple corrections for reliability. Furthermore, compared with previously reported INTERSALT values, the estimated mean change in systolic pressure per unit of change in body mass index decreased by about 5% and that for consumption of > or = 300 ml of absolute alcohol per week increased by about 6%. These results further clarify the observed INTERSALT associations of systolic blood pressure with 24-hour urinary sodium and potassium excretion, body mass index, and alcohol intake.

Adult↗
PubMed1994

Propofol-fentanyl anesthesia: a comparison with isoflurane-fentanyl anesthesia in coronary artery bypass grafting and valve replacement surgery.

The hemodynamic effects of propofol-fentanyl and isoflurane-fentanyl anesthesia during the prebypass period were compared in 42 patients undergoing coronary artery bypass grafting (CABG) and 22 patients undergoing valve replacement (VR) for stenotic lesions. Anesthesia was induced with fentanyl, 25 micrograms/kg, and pancuronium, 0.1 mg/kg, and was maintained with a propofol infusion commenced at 4 mg/kg/h (range 1 to 10 mg/kg/h) or with isoflurane commenced at 1% (range 0 to 2%). Additional fentanyl, 7.5 micrograms/kg, was given before sternotomy. Hemodynamic measurements were made before induction of anesthesia and at various times in the prebypass period. In the VR group, there were no significant differences between the two anesthetics in any hemodynamic variables during the study. Significant decreases (P < 0.05) in mean arterial pressure (MAP 14%), left ventricular stroke work index (LVSWI 29%), and stroke volume index (SVI 24%) occurred after 15 minutes of propofol anesthesia in the CABG group. With isoflurane MAP was well maintained with reductions in LVSWI and SVI of 22% and 20%, respectively. Isoflurane was, however, associated with a significant increase in heart rate (HR) in the CABG group (P < 0.05), whereas no significant change in HR occurred in CABG or VR patients receiving propofol. With both techniques there were no significant changes in right-sided or left-sided filling pressures or in systemic vascular resistance index in the CABG or VR groups, except for a decrease in pulmonary artery occlusion pressure in the propofol VR group and isoflurane CABG group at the time of aortic cannulation. Propofol produced similar hemodynamic changes in the CABG and VR groups. Both anesthetic techniques caused myocardial depression and effectively controlled the autonomic responses to sternotomy in both groups. The study suggests that propofol-fentanyl anesthesia is an acceptable technique for CABG surgery and for VR in patients with stenotic valvular heart disease.

Adolescent↗
PubMed1994

Body mass index and associations of sodium and potassium with blood pressure in INTERSALT.

This report further examines the relation of body mass index (BMI) to associations of 24-hour urinary sodium, potassium, and sodium-potassium ratio with blood pressure in INTERSALT, a 52-center international study of electrolytes and blood pressure. Analyses without adjustment for BMI indicated average systolic pressure greater by 6.00 mm Hg per 100 mmol higher sodium and diastolic by 2.52 mm Hg. With adjustment for BMI, these values were reduced to 3.14 and 0.14 mm Hg, respectively. For the sodium-potassium ratio, blood pressure associations were stronger when not adjusted for BMI, and for potassium, adjustment generally had little effect. To explore possible interactions of these variables with BMI in relation to blood pressure, the 52 centers were divided into two groups of 26 based on whether the center median for BMI was less than or greater than or equal to 24.5 kg/m2, and individuals within each of the 52 centers were classified into lower- or higher-BMI groups based on individual BMI less than or greater than or equal to 24.1 kg/m2. Sodium and the sodium-potassium ratio were positively and significantly and potassium inversely and significantly related to systolic pressure in all four of these subgroups, and the sodium-potassium ratio and potassium were related to diastolic pressure in two and three subgroups, respectively. Electrolyte-blood pressure associations did not differ significantly between the two subgroups of centers or between the two subgroups based on individuals.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Nutritional factors in blood pressure.

High sodium intake, low potassium intake, high body mass index and high alcohol intake are established risk factors for high blood pressure (BP) in populations. For sodium, an overview of randomised controlled trials gave the estimate that reduction in sodium of around 70 mmol per day lowered BP on average by 2.9 mmHg systolic and 1.6 mmHg diastolic. An overview of within-population epidemiological studies (excluding INTERSALT), with correction for regression dilution, gave a pooled (simple) regression estimate that 100 mmol lower sodium was associated with BP lower by 4.5 mmHg systolic and 2.5 mmHg diastolic. In INTERSALT, across centres, average sodium excretion was significantly related to slope of BP with age, such that 100 mmol lower sodium was associated with 10 mmHg lower rise in SBP over 30 years; among individuals, previous estimates of the size of relationships of sodium and potassium to BP in INTERSALT were too low because of insufficient correction for the 'regression dilution' problem. For sodium, revised corrected regression estimates, with adjustment for age and sex, were 4.3 mmHg/100 mmol for SBP and 1.8 mmHg/100 mmol for DBP. After adjustment for other confounders, the corrected SBP-sodium regression estimate was 3.1 mmHg/100 mmol; it was 6.0 mmHg/100 mmol if body mass index was excluded from the regression model. The revised multiply adjusted regression estimate for SBP and potassium was -0.67 mmHg/10 mmol. Body mass index was positively related to BP in INTERSALT, consistent with other studies; on average, regression coefficients indicated 3.0 mmHg lower SBP and 2.2 mmHg lower DBP, for body weight lower by 10 kg.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗