Showing papers on "Confidence interval published in 1991"

Postmenopausal estrogen therapy and cardiovascular disease. Ten-year follow-up from the nurses' health study.

Abstract: Background The effect of postmenopausal estrogen therapy on the risk of cardiovascular disease remains controversial. Our 1985 report in the Journal, based on four years of follow-up, suggested that estrogen therapy reduced the risk of coronary heart disease, but a report published simultaneously from the Framingham Study suggested that the risk was increased. In addition, studies of the effect of estrogens on stroke have yielded conflicting results. Methods We followed 48,470 postmenopausal women, 30 to 63 years old, who were participants in the Nurses' Health Study, and who did not have a history of cancer or cardiovascular disease at base line. During up to 10 years of follow-up (337,854 person-years), we documented 224 strokes, 405 cases of major coronary disease (nonfatal myocardial infarctions or deaths from coronary causes), and 1263 deaths from all causes. Results After adjustment for age and other risk factors, the overall relative risk of major coronary disease in women currently taking estrogen was 0.56 (95 percent confidence interval, 0.40 to 0.80); the risk was significantly reduced among women with either natural or surgical menopause. We observed no effect of the duration of estrogen use independent of age. The findings were similar in analyses limited to women who had recently visited their physicians (relative risk, 0.45; 95 percent confidence interval, 0.31 to 0.66) and in a low-risk group that excluded women reporting current cigarette smoking, diabetes, hypertension, hypercholesterolemia, or a Quetelet index above the 90th percentile (relative risk, 0.53; 95 percent confidence interval, 0.31 to 0.91). The relative risk for current and former users of estrogen as compared with those who had never used it was 0.89 (95 percent confidence interval, 0.78 to 1.00) for total mortality and 0.72 (95 percent confidence interval, 0.55 to 0.95) for mortality from cardiovascular disease. The relative risk of stroke when current users were compared with those who had never used estrogen was 0.97 (95 percent confidence interval, 0.65 to 1.45), with no marked differences according to type of stroke. Conclusions Current estrogen use is associated with a reduction in the incidence of coronary heart disease as well as in mortality from cardiovascular disease, but it is not associated with any change in the risk of stroke.

Aspirin use and reduced risk of fatal colon cancer

Abstract: Background and Methods. Experiments in animals and two epidemiologic studies in humans suggest that aspirin and other nonsteroidal antiinflammatory drugs (NSAIDs) may be protective against colon cancer. We tested this hypothesis in a prospective mortality study of 662,424 adults who provided information in 1982 on the frequency and duration of their aspirin use. Death rates from colon cancer were measured through 1988. The possible influence of other risk factors for colon cancer was examined in multivariate analyses for 598 case patients and 3058 matched control subjects drawn from the cohort. Results. Death rates from colon cancer decreased with more frequent aspirin use in both men and women. The relative risk among persons who used aspirin 16 or more times per month for at least one year was 0.60 in men (95 percent confidence interval, 0.40 to 0.89) and 0.58 in women (95 percent confidence interval, 0.37 to 0.90). The risk estimates were unaffected when we excluded persons who reported at ent...

Ultrasonographically assessed carotid morphology and the risk of coronary heart disease.

Abstract: As ultrasonographically assessed carotid arteriosclerosis is being used as a surrogate measure for coronary arteriosclerosis, we performed a prospective longitudinal study of the association of our high-resolution ultrasound assessment of extracranial carotid morphology with the risk of acute coronary events in 1,288 eastern Finnish men. The presence of any structural changes in the common carotid arteries or carotid bulbs was associated with a 3.29-fold (95% confidence interval, 1.31-8.29; p = 0.0074), intimal-medial thickening with a 2.17-fold (95% confidence interval, 0.70-6.74; p = NS), small carotid plaques with a 4.15-fold (95% confidence interval, 1.51-11.47; p less than 0.01), and large ("stenotic") plaques with a 6.71-fold (95% confidence interval, 1.33-33.91; p less than 0.01) risk of acute myocardial infarction compared with men free of any structural changes in the carotid artery wall at baseline. These data confirm the close relation between carotid artery wall morphology and coronary heart disease.

Risk factors for falls as a cause of hip fracture in women

Abstract: Background. Although even in the elderly most falls are not associated with fractures, over 90 percent of hip fractures are the result of a fall. Few studies have assessed whether the risk factors for falls are also important risk factors for hip fracture. Methods. To examine the importance of risk factors for falls in the epidemiology of hip fracture, we performed a case–control study of 174 women (median age, 80 years) admitted with a first hip fracture to 1 of 30 hospitals in New York and Philadelphia. Controls, matched to the case patients according to age and hospital, were selected from general surgical and orthopedic surgical hospital services. Information was obtained by direct interview. Results. As measured by the odds ratio, increased risks for hip fracture were associated with lower-limb dysfunction (odds ratio = 1.7; 95 percent confidence interval, 1.1 to 2.8), visual impairment (odds ratio = 5.1; 95 percent confidence interval, 1.9 to 13.9), previous stroke (odds ratio = 2.0; 95 per...

Estimation of heritability and prediction of selection response in plant populations

Abstract: A unified presentation, a synthesis, and an evaluation of the methods employed in the estimation of heritability in plants are presented. Asexual, cross‐fertilizing, and self‐fertilizing diploid species, as well as annual and perennial ones, are considered. All broad‐ and narrow‐sense heritabilities are defined on individual and family bases for prediction of response to selection for a target population of environments in space and time. Narrow‐sense heritabilities are defined in cross‐fertilizing species for expected response to variations of mass, half‐sib, and full‐sib family selection for the next generation and the long term, and similarly in self‐fertilizing species. The use of both collateral and lineal relatives to estimate heritability is discussed, and the biases present in the estimators are given. Many departures and variations of the common procedures are discussed. The standard errors of heritability estimators and confidence intervals are presented.

Statistical Intervals: A Guide for Practitioners

Abstract: Presents a detailed exposition of statistical intervals and emphasizes applications in industry. The discussion differentiates at an elementary level among different kinds of statistical intervals and gives instruction with numerous examples and simple math on how to construct such intervals from sample data. This includes confidence intervals to contain a population percentile, confidence intervals on probability of meeting specified threshold value, and prediction intervals to include observation in a future sample. Also has an appendix containing computer subroutines for nonparametric statistical intervals.

Ultrasonographically assessed carotid morphology and the risk of coronary heart disease.

Abstract: As ultrasonographically assessed carotid arteriosclerosis is being used as a surrogate measure for coronary arteriosclerosis, we performed a prospective longitudinal study of the association of our high-resolution ultrasound assessment of extracranial carotid morphology with the risk of acute coronary events in 1,288 eastern Finnish men. The presence of any structural changes in the common carotid arteries or carotid bulbs was associated with a 3.29-fold (95% confidence interval, 1.31-8.29; p = 0.0074), intimal-medial thickening with a 2.17-fold (95% confidence interval, 0.70-6.74; p = NS), small carotid plaques with a 4.15-fold (95% confidence interval, 1.51-11.47; p less than 0.01), and large ("stenotic") plaques with a 6.71-fold (95% confidence interval, 1.33-33.91; p less than 0.01) risk of acute myocardial infarction compared with men free of any structural changes in the carotid artery wall at baseline. These data confirm the close relation between carotid artery wall morphology and coronary heart d...

Relation between malpractice claims and adverse events due to negligence. Results of the Harvard Medical Practice Study III.

Abstract: Background and Methods. By matching the medical records of a random sample of 31,429 patients hospitalized in New York State in 1984 with statewide data on medical-malpractice claims, we identified patients who had filed claims against physicians and hospitals. These results were then compared with our findings, based on a review of the same medical records, regarding the incidence of injuries to patients caused by medical management (adverse events). Results. We identified 47 malpractice claims among 30,195 patients' records located on our initial visits to the hospitals, and 4 claims among 580 additional records located during follow-up visits. The overall rate of claims per discharge (weighted) was 0.13 percent (95 percent confidence interval, 0.076 to 0.18 percent). Of the 280 patients who had adverse events caused by medical negligence as defined by the study protocol, 8 filed malpractice claims (weighted rate, 1.53 percent; 95 percent confidence interval, 0 to 3.2 percent). By contrast, our estimate...

Back disorders and nonneutral trunk postures of automobile assembly workers.

Abstract: A case-referent study was conducted in an automobile assembly plant to evaluate the health effect of trunk postures, such as bending and twisting, that deviate from anatomically neutral. Cases of back disorders were all those of workers who reported back pain to the medical department in a ten-month period and met the severity criteria of an interview. The referents were randomly selected workers free of back pain according to medical department records, an interview, and an examination. For each of the final 95 cases and 124 referents, the job was analyzed for postural and lifting requirements with a video recording and software analysis system by analysts blinded to the case/referent status. Back disorders were associated with mild trunk flexion [odds ratio (OR) 4.9, 95% confidence interval (95% CI) 1.4-17.4], severe trunk flexion (OR 5.7, 95% CI 1.6-20.4), and trunk twist or lateral bend (OR 5.9, 95% CI 1.6-21.4). The risk increased with exposure to multiple postures and increasing duration of exposure.

Determination of confidence limits for experiments with low numbers of counts

Abstract: Two different methods, classical and Bayesian, for determining confidence intervals involving Poisson-distributed data are compared. Particular consideration is given to cases where the number of counts observed is small and is comparable to the mean number of background counts. Reasons for preferring the Bayesian over the classical method are given. Tables of confidence limits calculated by the Bayesian method are provided for quick reference.

In-hospital and 1-year mortality in 1,524 women after myocardial infarction. Comparison with 4,315 men.

Abstract: We determined in-hospital and 1-year prognoses after acute myocardial infarction (MI) in 5,839 consecutive patients derived from 14 of 21 coronary care units in Israel during 1981-1983. Age-adjusted in-hospital mortality was 23.1% in 1,524 women and 15.7% in 4,315 men (p less than 0.0005). One-year age-adjusted mortality rates in patients surviving hospitalization were 11.8% in women and 9.3% in men (p = 0.03). Cumulative age-adjusted 1-year mortality rates were 31.8% in women and 23.1% in men (p less than 0.0005). Relative odds of mortality, covariate-adjusted for major prognostic factors that included age, prior MI, congestive heart failure, and infarct location by electrocardiogram, indicated that female gender was independently and significantly associated with increased mortality both during hospitalization (relative odds, 1.72; 95% confidence interval, 1.45-2.04) and at 1 year after discharge (relative odds, 1.32; 95% confidence interval, 1.05-1.66). In separate multivariate analyses for each gender, a major factor that emerged as a predictor of outcome in women, but not in men, was a reported history of diabetes mellitus, both for in-hospital mortality and for 1-year mortality. However, even in the nondiabetics in this population, female gender was a significant, independent predictor of in-hospital mortality. The findings of the present study substantiate that women fare worse than men after suffering an acute MI, that increased age does not fully account for the increased mortality in women, and that diabetic women are at particularly high risk once MI has occurred.

Statistical treatment for rejection of deviant values : critical values of Dixon's Q parameter and related subrange ratios at the 95% confidence level

Abstract: Critical values at the 95% confidence level for the two-tailed Q test, and related tests based upon subrange ratios, for the statistical rejection of outlying data have been interpolated by applying cubic regression analysis to the values originally published by Dixon. Corrections to errors in Dixon's original tables are also included. It is recommended that the newly generated 95% critical values be adopted by analytical chemists as the general standard for the rejection of outlier values

A Maximum Likelihood Method for Estimating Genome Length Using Genetic Linkage Data

Abstract: The genetic length of a genome, in units of Morgans or centimorgans, is a fundamental characteristic of an organism. We propose a maximum likelihood method for estimating this quantity from counts of recombinants and nonrecombinants between marker locus pairs studied from a backcross linkage experiment, assuming no interference and equal chromosome lengths. This method allows the calculation of the standard deviation of the estimate and a confidence interval containing the estimate. Computer simulations have been performed to evaluate and compare the accuracy of the maximum likelihood method and a previously suggested method-of-moments estimator. Specifically, we have investigated the effects of the number of meioses, the number of marker loci, and variation in the genetic lengths of individual chromosomes on the estimate. The effect of missing data, obtained when the results of two separate linkage studies with a fraction of marker loci in common are pooled, is also investigated. The maximum likelihood estimator, in contrast to the method-of-moments estimator, is relatively insensitive to violation of the assumptions made during analysis and is the method of choice. The various methods are compared by application to partial linkage data from Xiphophorus.

Statistics for the Life Sciences

Abstract: 1. Introduction. Statistics and the Life Sciences. Examples and Overview. 2. Description of Populations and Samples. Introduction. Frequency Distributions: Techniques for Data. Frequency Distributions: Shapes and Examples. Descriptive Statistics: Measures of Center. Boxplots. Measures of Dispersion. Effect of Transformation of Variables (Optional). Samples and Populations: Statistical Inference. Perspective. 3. Random Sampling, Probability, and the Binomial Distribution. Probability and the Life Sciences. Random Sampling. Introduction to Probability. Probability Trees. Probability Rules (Optional). Density Curves. Random Variables. The Binomial Distribution. Fitting a Binomial Distribution to Data (Optional). 4. The Normal Distribution. Introduction. The Normal Curves. Areas Under a Normal Curve. Assessing Normality. The Continuity Correction (Optional). Perspective. 5. Sampling Distributions. Basic Ideas. Dichotomous Observations. Quantitative Observations. Illustration of the Central Limit Theorem (Optional). The Normal Approximation to the Binomial Distribution (Optional). Perspective. 6. Confidence Intervals. Statistical Estimation. Standard Error of the Mean. Confidence Interval. Planning a Study to Estimate. Conditions for Validity of Estimation Methods. Confidence Interval for a Population Proportion. Perspective and Summary. 7. Comparison of Two Independent Samples. Introduction. Standard Error of (y1 - y2). Confidence Interval. Hypothesis Testing: The t-test. Further Discussion of the t-test. One-Tailed Tests. More on Interpretation of Statistical Significance. Planning for Adequate Power (Optional). Student's t: Conditions and Summary. More on Principles of Testing Hypotheses. The Wilcoxon-Mann-Whitney Test. Perspective. 8. Statistical Principles of Design. Introduction. Observational Studies. Experiments. Restricted Randomization: Blocking and Stratification. Levels of Replication. Sampling Concerns (Optional). Perspective. 9. Comparison of Paired Samples. Introduction. The Paired-Sample t-Test and Confidence Interval. The Paired Design. The Sign Test. The Wilcoxon Signed-Rank Test. Further Considerations in Paired Experiments. Perspective. 10. Analysis of Categorical Data. Inference for Proportions: The Chi-Squared Goodness-of-Fit Test. The Chi-Squared Test for a 2 X 2 Contingency Table. Independence and Association in a 2 X 2 Contingency Table. Fisher's Exact Test (Optional). The r x k Contingency Table. Applicability of Methods. Confidence Interval for a Difference Between Proportions. Paired Data and 2 X 2 Tables (Optional). Relative Risk and the Odds Ratio (Optional). Summary of Chi-Squared Tests. 11. Comparing the Means of Many Independent Samples. Introduction. The Basic Analysis of Variance. The Analysis of Variance Model (Optional). The Global F-Test. Applicability of Methods. Two-Way ANOVA (Optional). Linear Combinations of Means (Optional). Multiple Comparisons (Optional). Perspective. 12. Linear Regression and Correlation. Introduction. The Fitted Regression Line. Parametric Interpretation of Regression: The Linear Model. Statistical Inference Concerning B1. The Correlation Coefficient. Guidelines for Interpreting Regression and Correlation. Perspective. Summary of Formulas. 13. A Summary of Inference Methods. Introduction. Data Analysis Samples. Appendices. Chapter Notes. Statistical Tables. Answers to Selected Exercises. Index. Index of Examples.

Confidence intervals for weighted sums of poisson parameters

Abstract: Directly standardized mortality rates are examples of weighted sums of Poisson rate parameters. If the numbers of events are large then normal approximations can be used to calculate confidence intervals, but these are inadequate if the numbers are small. We present a method for obtaining approximate confidence limits for the weighted sum of Poisson parameters as linear functions of the confidence limits for a single Poisson parameter, the unweighted sum. The location and length of the proposed interval depend on the method used to obtain confidence limits for the single parameter. Therefore several methods for obtaining confidence intervals for a single Poisson parameter are compared. For single parameters and for weighted sums of parameters, simulation suggests that the coverage of the proposed intervals is close to the nominal confidence levels. The method is illustrated using data on rates of myocardial infarction obtained as part of the WHO MONICA Project in Augsburg, Federal Republic of Germany.

Familial Aggregation of Alzheimer's Disease and Related Disorders: A Collaborative Re-Analysis of Case-Control Studies

Abstract: Case-control studies of Alzheimer's disease were re-analysed to examine the association of Alzheimer's disease with family history in first degree relatives of dementia, Down's syndrome and Parkinson's disease. Overall, the relative risk of Alzheimer's disease for those with at least one first degree relative with dementia was 3.5 (95% confidence interval 2.6-4.6). Stratification according to age of onset of Alzheimer's disease showed that the relative risk decreased with increasing onset age. However, among patients with an onset of disease after 80 years, there were still significantly more subjects with one or more first degree relatives with dementia as compared to controls (relative risk 2.6; 95% confidence interval 1.3-5.2). The relative risk of Alzheimer's disease was significantly lower in patients who had one first degree relative with dementia (relative risk 2.6; 95% confidence interval 2.0-3.5) as compared to those who had two or more affected relatives (relative risk 7.5; 95% confidence interval 3.3-16.7). Furthermore, the re-analysis showed a significant association between Alzheimer's disease and family history of Down's syndrome (relative risk 2.7; 95% confidence interval 1.2-5.7), which was strongest in those patients who had a positive family history of dementia. The relative risk of Alzheimer's disease for those with a positive family history of Parkinson's disease was 2.4 (95% confidence interval 1.0-5.8).

High-Fat, Low-Carbohydrate Diet and the Etiology of Non-Insulin-dependent Diabetes Mellitus: The San Luis Valley Diabetes Study

Abstract: Diet has long been believed to be an important risk factor for non-insulin-dependent diabetes. Animal studies generally support a relation between high-fat diets and development of insulin resistance. However, conclusive epidemiologic evidence is lacking. To further investigate the role of dietary fat and carbohydrate as potential risk factors for the onset of non-insulin-dependent diabetes mellitus, current diet was assessed among a geographically based group of 1,317 subjects without a prior diagnosis of diabetes who were seen in the period from 1984 to 1988 in two countries in southern Colorado. In this study, 24-hour diet recalls were reported prior to an oral glucose tolerance test. Persons with previously undiagnosed diabetes (n = 70) and impaired glucose tolerance (n = 171) were each compared with confirmed normal controls (n = 1,076). The adjusted odds ratios relating a 40-g/day increase in fat intake to non-insulin-dependent diabetes mellitus and impaired glucose tolerance were 1.51 (95% confidence interval 0.85-2.67) and 1.62 (95% confidence interval 1.09-2.41), respectively. Restricting cases to diabetic persons with fasting glucose greater than 140 mg/dl and persons with impaired glucose tolerance confirmed on follow-up, the odds ratios increased to 3.03 (95% confidence interval 1.07-8.62) and 2.67 (95% confidence interval 1.33-5.36), respectively. The findings support the hypothesis that high-fat, low-carbohydrate diets are associated with the onset of non-insulin-dependent diabetes mellitus in humans.

Complications of pregnancy and delivery in relation to psychosis in adult life: data from the British perinatal mortality survey sample.

Abstract: OBJECTIVE--To evaluate whether events occurring at or around the time of birth contribute to the onset of psychotic illness in adult life DESIGN-Pregnancy and birth complications as possible causes of adult mental illness were studied in the population sample of the British perinatal mortality survey Subsequent psychiatric admissions were independently identified through the Mental Health Enquiry and records of regional and special health authorities Logistic regression was used to compare data on perinatal deaths with those on survivors to determine factors independently associated with perinatal death, and this equation was then used to calculate the risk of perinatal death for each survivor SUBJECTS--16,980 people born in a single week in 1958 (the British perinatal mortality survey sample), including 252 patients admitted to psychiatric care; case notes of 235 patients were supplied MAIN OUTCOME MEASURES AND RESULTS--Patients with a schizophrenic illness (whether defined by "broad" (n = 57) or "narrow" (n = 35) diagnostic criteria) did not have a greater mean risk of perinatal death than the population in general, but there was some evidence of increased liability (relative risk 243; 95% confidence interval 117 to 505) for those with affective psychosis (n = 32) Specific high risk variables for affective psychosis were decreased gestation time (2739 v 2812 days; mean difference 73 days, 95% confidence interval 31 to 115; p less than 0002) and prescription of vitamin K to the child in the first week of life (19% of patients v 5% of controls, p = 0016) CONCLUSIONS--The findings give no support to theories that factors predicting perinatal mortality contribute significantly to causation of schizophrenic illness Further investigation of decreased gestation length in relation to affective disorder is required

Confidence Intervals for the Largest Autoresgressive Root in U.S. Macroeconomic Time Series

Abstract: This paper provides asymptotic confidence intervals for the largest autoregressive root of a time series when this root is close to one. The intervals are readily constructed either graphically or using tables in the Appendix. When applied to the Nelson-Plosser (1982) data set, the main conclusion is that the confidence intervals typically are wide. The conventional emphasis on testing for whether the largest root equals one fails to convey the substantial sampling variability associated with this measure of persistence.

A Case-Control Study of Diet and Cancer of the Pancreas

Abstract: In a population-based case-control study carried out in Adelaide, South Australia, during the years 1984-1987, the diets of 104 cases of cancer of the pancreas 1 year prior to diagnosis were compared with the diets of 253 community controls. A quantitative food-frequency questionnaire was used to assess usual dietary intakes of 179 food items. Cases were compared with controls in terms of both the amounts of individual food items consumed and the estimated contributions of 48 nutrients to the diet. Food items consumed more by cases than controls included boiled eggs and omelettes as well as a number of items that could be collectively described as sweet and fatty. Food items consumed less by cases than controls included several vegetables and fruits. Conditional logistic regression analysis of nutrient intake adjusted for total energy and for alcohol and tobacco usage yielded an estimate of relative risk of 3.19, with a 95% confidence interval of 1.58-6.47 for the highest quartile of cholesterol intake (relative to the lowest quartile). For the top quartile of refined sugar intake, the estimated relative risk was 2.21 (95% confidence interval 1.07-4.55). Several nutrients derived principally from plant foods were statistically significantly associated with lower risks. Alcohol consumption was significantly lower among cases than controls. Current smokers had a relative risk of 1.76 (95% confidence interval 0.93-3.34) relative to those who had never smoked. There was no association of pancreatic cancer with coffee drinking.

Medical history and the risk of Alzheimer's disease: a collaborative re-analysis of case-control studies. EURODEM Risk Factors Research Group.

Abstract: In a re-analysis of eight case-control studies on Alzheimer's disease we explored several medical conditions that had previously been suggested as possible risk factors for Alzheimer's disease. History of hypothyroidism was increased in cases as compared to controls (relative risk 2.3; 95% confidence interval 1.0-5.4). Severe headaches and migraine were inversely related to Alzheimer's disease (relative risk 0.7; 95% confidence interval 0.5-1.0). More cases than controls reported epilepsy before onset of Alzheimer's disease (relative risk 1.6; 95% confidence interval 0.7-3.5), especially for epilepsy with an onset within 10 years of onset of dementia. Neurotropic viruses, allergic conditions, general anaesthesia and blood transfusions were not associated with Alzheimer's disease.

Epidemiological evidence for age-dependent regression of pre-invasive cervical cancer.

Abstract: Data from the screening programme in British Columbia are used to test hypotheses about the natural history of cervical cancer, especially about progression and regression of preclinical lesions (dysplasia and carcinoma in situ). Three models are considered. A model without regression does not give an adequate fit of the data (P less than 0.001), and results in an implausible estimate of 33 years for the mean duration of pre-invasive lesions. A model with an equal regression rate at all ages still does not result in a good reproduction of the data. A good fit is achieved for a model with different regression rates in lesions that develop under and over age 34. Under age 34, 84% of the new lesions will regress spontaneously, with a 95% confidence interval of 76-92% regression. Over age 34, we estimate that 40% of the new lesions will regress. The average duration of dysplasia + CIS is 11.8 years, and the sensitivity of the Pap-smear is 80%. It is concluded that a considerable proportion of pre-invasive lesions in young women do not progress. The findings about progression and duration of pre-invasive lesions do not support the still prevailing tendency of frequently making Pap smears in young women.